Add agent semantic conventions

Resolves open-telemetry#396

docs/attributes-registry/agent.md

@@ -0,0 +1,18 @@
+<!--- Hugo front matter used to generate the website version of this page:
+--->
+
+# Agent
+
+## Agent Attributes
+
+<!-- semconv registry.agent(omit_requirement_level) -->
+| Attribute  | Type | Description  | Examples  | Stability |
+|---|---|---|---|---|
+| `agent.distro` | string | Agent distribution. [1] | `github.com/signalfx/splunk-otel-collector`; `github.com/aws-observability/aws-otel-collector` | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
+| `agent.type` | string | Agent type. [2] | `io.opentelemetry.collector`; `com.dynatrace.one_agent`; `com.newrelic.infra_agent` | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
+| `agent.version` | string | The version string of the agent. The format is not defined by these conventions. | `2.0.0`; `a01dbef8a` | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
+
+**[1]:** An identifier that identifies the distribution of the agent. A number of distributions can belong to the same agent.type. For example OpenTelemetry Collector has multiple known distributions, e.g. github.com/signalfx/splunk-otel-collector,  github.com/aws-observability/aws-otel-collector, etc.  The value is typically a URL where the agent's source code is hosted  (without the preceding http/https scheme). However other approaches for choosing agent.distro values are also valid (e.g. reverse FQDN).
+
+**[2]:** A string that uniquely identifies the agent type. A recommended way to choose a value is to pick a reverse FQDN of a domain that is under the control of the agent's author. Must remain unchanged between different versions of the same agent type.
+<!-- endsemconv -->

docs/resource/agent.md

@@ -0,0 +1,18 @@
+<!--- Hugo front matter used to generate the website version of this page:
+--->
+
+# Agent
+
+## Agent Attributes
+
+<!-- semconv agent(full) -->
+| Attribute  | Type | Description  | Examples  | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability |
+|---|---|---|---|---|---|
+| [`agent.type`](../attributes-registry/agent.md) | string | Agent type. [1] | `io.opentelemetry.collector`; `com.dynatrace.one_agent`; `com.newrelic.infra_agent` | `Required` | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
+| [`agent.distro`](../attributes-registry/agent.md) | string | Agent distribution. [2] | `github.com/signalfx/splunk-otel-collector`; `github.com/aws-observability/aws-otel-collector` | `Recommended` | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
+| [`agent.version`](../attributes-registry/agent.md) | string | The version string of the agent. The format is not defined by these conventions. | `2.0.0`; `a01dbef8a` | `Recommended` | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
+
+**[1]:** A string that uniquely identifies the agent type. A recommended way to choose a value is to pick a reverse FQDN of a domain that is under the control of the agent's author. Must remain unchanged between different versions of the same agent type.
+
+**[2]:** An identifier that identifies the distribution of the agent. A number of distributions can belong to the same agent.type. For example OpenTelemetry Collector has multiple known distributions, e.g. github.com/signalfx/splunk-otel-collector,  github.com/aws-observability/aws-otel-collector, etc.  The value is typically a URL where the agent's source code is hosted  (without the preceding http/https scheme). However other approaches for choosing agent.distro values are also valid (e.g. reverse FQDN).
+<!-- endsemconv -->

model/registry/agent.yaml

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+groups:
+  - id: registry.agent
+    prefix: agent
+    type: attribute_group
+    brief: >
+        An agent.
+    attributes:
+      - id: type
+        type: string
+        stability: experimental
+        brief: >
+          Agent type.
+        examples: [io.opentelemetry.collector,com.dynatrace.one_agent,com.newrelic.infra_agent]
+        note: >
+          A string that uniquely identifies the agent type. A recommended way to choose
+          a value is to pick a reverse FQDN of a domain that is under the control of the
+          agent's author. Must remain unchanged between different versions of the same
+          agent type.
+          
+      - id: version
+        type: string
+        stability: experimental
+        brief: >
+          The version string of the agent. The format is not defined by these conventions.
+        examples: ["2.0.0", "a01dbef8a"]
+
+      - id: distro
+        type: string
+        stability: experimental
+        brief: >
+          Agent distribution.
+        examples: [github.com/signalfx/splunk-otel-collector, github.com/aws-observability/aws-otel-collector]
+        note: >
+          An identifier that identifies the distribution of the agent. A number of
+          distributions can belong to the same agent.type. For example OpenTelemetry
+          Collector has multiple known distributions, e.g. github.com/signalfx/splunk-otel-collector, 
+          github.com/aws-observability/aws-otel-collector, etc. 
+          The value is typically a URL where the agent's source code is hosted 
+          (without the preceding http/https scheme). However other approaches for choosing
+          agent.distro values are also valid (e.g. reverse FQDN).

model/resource/agent.yaml

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+groups:
+  - id: agent
+    prefix: agent
+    type: resource
+    brief: >
+        An agent
+    attributes:
+      - ref: agent.type
+        requirement_level: required
+      - ref: agent.version
+      - ref: agent.distro