[#266] services/tree: Add sync check

Do not accept requests until initial sync is finished.
`Apply` is deliberately left out -- we don't want to miss anything new.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/services/tree/sync.go

@@ -388,7 +388,7 @@ func (s *Service) syncLoop(ctx context.Context) {
 				s.log.Error(logs.TreeCouldNotFetchContainers, zap.Error(err))
 				s.metrics.AddSyncDuration(time.Since(start), false)
 				span.End()
-				continue
+				break
 			}
 
 			newMap, cnrsToSync := s.containersToSync(cnrs)
@@ -402,6 +402,7 @@ func (s *Service) syncLoop(ctx context.Context) {
 			s.metrics.AddSyncDuration(time.Since(start), true)
 			span.End()
 		}
+		s.initialSyncDone.Store(true)
 	}
 }