Defer permissions check on GetTelemetrySources (istio#406)

Author: toffentoffen

tsb/observability/v2/telemetry_source_service.pb.go

@@ -26,7 +26,7 @@ service TelemetrySources {
   // Get the details of an existing telemetry source.
   rpc GetTelemetrySource(GetTelemetrySourceRequest) returns (tsb.observability.v2.TelemetrySource){
     option (tetrateio.api.tsb.rbac.v2.requires) = {
-      permissions: READ
+      defer_permission_check_to_application: true
     };
     option (google.api.http) = {
       get: "/v2/{fqn=organizations/**/telemetry/sources/*}"