chore: mention usage data reporting in AI Gov docs (#21664)

<!--

If you have used AI to produce some or all of this PR, please ensure you
have read our [AI Contribution
guidelines](https://coder.com/docs/about/contributing/AI_CONTRIBUTING)
before submitting.

-->

docs/ai-coder/usage-data-reporting.md

@@ -0,0 +1,48 @@
+# Usage Data Reporting
+
+The [AI Governance Add-On](./ai-governance.md) requires reporting usage data to Tallyman, a Coder-managed server for billing and reporting purposes. Coder only captures and sends the following information, related to your deployment ID:
+
+- number of agent workspace builds consumed
+- number of AI governance seats consumed
+
+No user-identifiable information or additional metrics are sent to Tallyman. This information is also shared with [Metronome](https://metronome.com), a Stripe product and Coder partner for usage-based and reporting.
+
+To send usage data, your Coder deployment must be able to make outbound HTTPS requests to `https://tallyman-prod.coder.com`. Usage data is sent approximately every 17 minutes and can be monitored via `coderd` logs.
+
+Example of a successful request (requires debug logging enabled [`CODER_LOG_FILTER=.*`](../reference/cli/server.md#-l---log-filter)):
+
+```sh
+[debu] published usage events to tallyman accepted=5 rejected=0
+```
+
+Example of a request payload:
+
+```sh
+POST /api/v1/events/ingest HTTP/1.1
+Host: tallyman-prod.coder.com
+Content-Type: application/json
+Coder-License-Key: <license-jwt> # your license JWT for verification
+Coder-Deployment-ID: 8a4e92f1-3b7c-4d5e-9f12-abc123def456 # your deployment ID
+
+{
+  "events": [
+    {
+      "id": "550e8400-e29b-41d4-a716-446655440000", # unique event ID generated by Coder
+      "event_type": "dc_managed_agents_v1", # aka. agent workspace builds
+      "event_data": {
+        "count": 1
+      },
+      "created_at": "2025-01-15T14:30:00Z"
+    }
+  ]
+}
+```
+
+Example of a failed request (e.g. Tallyman Server is blocked by your network):
+
+```sh
+[warn] failed to send publish request to tallyman count=5 error="Post \"https://tallyman-prod.coder.com/api/v1/events/ingest\": dial tcp: lookup tallyman-prod.coder.com: no such host"
+```
+
+> [!NOTE]
+> Air-gapped deployments and/or those with legal restrictions around usage reporting can [contact us](https://coder.com/contact) to discuss alternative methods.