updated agent documentation + moved agent to data collection

docs/data-collection/zabbix-agent.md

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+# Zabbix Agent
+
+In this topic we will talk about the Zabbix agent. The Zabbix agent is a native agent made by Zabbix that we can deploy on different Operating Systems and that supports a wide range of build-in items keys.
+Zabbix has 2 agents we have the ```Zabbix agent``` and we have the ```Zabbix agent 2``` So when you read in this book about the ```Zabbix agent``` we talk about the 1st agent. This can sound a bit
+weird having 2 agents but it's not. The agent was developed years ago when zabbix was first released and is written in C the agent 2 is written in GO and is developed next to the Agent 1.
+We will see later what the advantages and disadvantages are of both and give you tips to choose the agent that fits best for you.
+To make things more complex both agents can be configure to work in ```active``` or in ```passive``` mode or in both.
+When we create an item on our host and we want to use the item that works with our Zabbix agent we have 2 options to choose from.
+
+![active-passive agent](image/agent/zabbix-agent-active-passive.png)
+
+We can create items that are active or passive depending on how our agent has been configured.
+A zabbix agent can either be active or passive or both active and passive.
+
+???+ Note
+    Zabbix 7.0 is backwards compatible with agents back to 1.4 but of course newer item keys added after 1.4 will not be recognized in those older agents. So if you like to use the new items keys it's best to upgrade your agents when you can.
+
+Sometimes there are cases when the item keys provided by Zabbix are just not enough.
+
+In this case it's possible to extend our agents with UserParameters.
+This allows us to extend the agent with our own keys based on scripts that we make to extend our agents. This is something we cover in the topic ```UserParameters```.
+
+Zabbix has a huge list of items keys it supports on linux but when we select our item keys we have to careful read the documentation careful as some items keys are OS specific. For example there are item keys that only work on MS Windows.
+
+[https://www.zabbix.com/documentation/7.0/en/manual/config/items/itemtypes/zabbix_agent/win_keys](https://www.zabbix.com/documentation/7.0/en/manual/config/items/itemtypes/zabbix_agent/win_keys)
+
+Some item keys can only be used on the new Agent 2.
+
+[https://www.zabbix.com/documentation/7.0/en/manual/config/items/itemtypes/zabbix_agent/zabbix_agent2](https://www.zabbix.com/documentation/7.0/en/manual/config/items/itemtypes/zabbix_agent/zabbix_agent2)
+
+Here is a list of the item keys that will work on Linux. But also here be careful as some things can be different depending on the OS or the kernel version.
+
+[https://www.zabbix.com/documentation/7.0/en/manual/config/items/itemtypes/zabbix_agent](https://www.zabbix.com/documentation/7.0/en/manual/config/items/itemtypes/zabbix_agent)
+
+When we want to add an item we can either lookup the item in the online documetation, try to remember it and just write it in the box or press the select button next to the item field. This will give a popup with a short explanation about what the items does.
+
+![select-box](image/agent/item-select.png)
+
+However you will see that it's lacking lots of information.
+My advice is to use the online documentation.
+
+So in this topic we will explain you all the differences :
+
+- Zabbix Agent (Legacy)
+- Zabbix Agent 2
+- Agent vs Agent 2
+- Active Agent
+- Passive Agent
+- Active vs Passive
+- Zabbix agent Linux
+- Zabbix agent Windows
+
+
+## Zabbix Agent (Legacy)
+
+Our Zabbix agent or the legacy agent can run on a whole set of supported platforms. At the time of writing the agent on Zabbix 7 supports:
+
+- Linux (Redhat, Suse, Ubuntu, Debian, Rocky, Alma, ...)
+- FreeBSD
+- Windows
+- MacOS
+- Raspberry Pi
+- HPUnix
+- OpenBSD
+- AIX
+- Solaris
+
+???+ info
+    A full up to date list can be found here https://www.zabbix.com/download
+
+The agent can be installed on a host to collect data from that host or from an application running on that host.
+The advantage is that the agent has a very small footprint and that we can extend the agent by creating our own scripts.
+Agents can work in active or in passive mode or can do this in both ways simultaniously.
+
+The legacy agent can be extended with modules that are written in C.
+
+
+
+
+
+
+## Zabbix Agent 2
+
+## Agent1 vs Agent2
+
+| Parameter 			| Agent					 | Agent 2 				|
+| :----				| :----					 |:----					|
+| Programming language 		| C					 | Go and some parts in C		|
+| Linux daemonization 		| Yes					 | By systemd only			|
+| Run as Windows service	| Yes					 | Yes					|
+| Supported extensions		| Loadable Modules in C	 		 | Plugins in Go			|
+| Supported platforms		| All					 | Linux, Window, any OS with GO	|
+| Concurrency			| Active checks are executed sequentialy | All check executed concurrently	|
+| Scheduled/flexible intervals	| Passive check only			 | Acive and Passsive checks		|
+| Persistent storage 		| No					 | Yes (SQLite3)			|
+| Timeout settings		| On agent level only			 | Plugins can override the timout	|
+| Changes user at runtime	| Yes (on Unix like sytems only)	 | No (controlled by SystemD		|
+| Cipersuits user configurable  | Yes					 | No					|
+
+???+ info
+    For more details bout the differences check the official documentation.
+    https://www.zabbix.com/documentation/6.0/en/manual/appendix/agent_comparison
+
+
+
+We can detect the generation from the agent by using the ```agent.variant``` item key this will return us if it is agent generation 1 or 2
+
+
+## Active Agent
+
+## Passive Agent
+
+## Active vs Passive
+
+## UserParameters
+
+## Zabbix agent Linux
+
+The agent can be installed on Linux in different ways. The most easy way however is probably installing the agent from Package.
+
+Most of the popular operating systems are supported by Zabbix and installation instrucations are provided on the Zabbix webpage when you go to https://www.zabbix.com/download
+
+Here we just have to choose that we like to install from Zabbix packages and choose our OS and the version. Then we just need to follow the instructions to add the repository to our OS. From here we can install the Agent.
+
+![choose OS](image/agent/agent-packages.png)
+
+After selecting the correct settings we get to see the instructions how to add our repo to the OS.
+
+![Add repo](image/agent/add-repo.png)
+
+In case your OS was not in the list there is still the option to download the agents pre compiled. Choose ```Zabbix agents``` and select your correct kernel version.
+
+![Add repo](image/agent/select-agent-archive.png)
+
+Then select the Zabbix release and press ```Download``` to get a binary version.
+
+![Add repo](image/agent/download-agent-archive.png)
+
+If all this fails then there is still the option to download the source and compile the agent yourself.
+
+
+## Zabbix agent windows