feat: add agentapi endpoint to report connections for audit (#16507)

This change adds a new `ReportConnection` endpoint to the `agentapi`.

The protocol version was bumped previously, so it has been omitted here.

This allows the agent to report connection events, for example when the
user connects to the workspace via SSH or VS Code.

Updates #15139

tailnet/proto/tailnet_drpc_old.go

@@ -36,7 +36,7 @@ type DRPCTailnetClient23 interface {
 }
 
 // DRPCTailnetClient24 is the Tailnet API at v2.4. It is functionally identical to 2.3, because the
-// change was to the Agent API (ResourcesMonitoring methods).
+// change was to the Agent API (ResourcesMonitoring and ReportConnection methods).
 type DRPCTailnetClient24 interface {
 	DRPCTailnetClient23
 }

tailnet/proto/version.go

@@ -43,6 +43,8 @@ import (
 //   - Shipped in Coder v2.{{placeholder}} // TODO Vincent: Replace with the correct version
 //   - Added support for GetResourcesMonitoringConfiguration and
 //     PushResourcesMonitoringUsage RPCs on the Agent API.
+//   - Added support for reporting connection events for auditing via the
+//     ReportConnection RPC on the Agent API.
 const (
 	CurrentMajor = 2
 	CurrentMinor = 4