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/gen/controller.swagger.json

@@ -3344,6 +3344,10 @@
           "format": "int32",
           "description": "Maximum number of connections allowed in a Session.  Unlimited is indicated by the value -1."
         },
+        "worker_filter": {
+          "type": "string",
+          "description": "Optional boolean expression to filter the workers that are allowed to satisfy this request."
+        },
         "attributes": {
           "type": "object",
           "description": "The attributes that are applicable for the specific Target."