Add worker tagging (#862)

This allows workers to have tags assigned to them, which can then be filtered to control which targets they are allowed to serve.

internal/proto/local/controller/servers/services/v1/server_coordination_service.proto

@@ -65,6 +65,12 @@ message StatusRequest {
 
   // Jobs which this worker wants to report the status.
   repeated JobStatus jobs = 20;
+
+  // Whether to update tags from the Server block on this RPC. We only need to
+  // do this at startup or (at some point) SIGHUP, so specifying when it's
+  // changed allows us to avoid constant database operations for something that
+  // won't change very often, if ever.
+  bool update_tags = 30;
 }
 
 enum CHANGETYPE {

internal/proto/local/controller/servers/services/v1/session_service.proto

@@ -33,6 +33,9 @@ service SessionService {
 message LookupSessionRequest {
 	// The session ID from the client
 	string session_id = 10;
+	// The name of the requesting worker, used for filtering to ensure this
+	// worker is allowed to handle this session.
+	string server_id = 20;
 }
 
 // LookupSessionResponse contains information necessary for a client to