#6261 add two vars to the alert template variable list

[rogin]

Adds "serverName" and "environmentName" to the alert template variable list.
Requires Java 9+.
Requires an update to the documentation.

Test procedure:

• Compile this patch with Java 9+ and start server
• Login and get past initial account setup
• Set Server Name and Environment Name under Settings tab
• Import and deploy the two attached channels
• Import the attached alert
• Open the imported alert and validate two additional options are present on the right-hand side: "serverName" and "environmentName"
• Validate the two additional options can be copied into the template text area
• Send any message to channel "throws error"
• Validate the resulting text in channel "Receiver" contains the Server Name and Environment Name as you defined in the Settings tab
• Clear the Server Name and Environment Name under Settings tab, then re-run a message to ensure the alert template's values are replaced with empty strings

throws error.xml.txt
Receiver.xml.txt
Foo alert.xml.txt