Gracefully shutdown grpc servers (#4897)

## Motivation
Closes #4867 

## Changes
Makes a call to graceful stop before force closing open connections.

## Test Plan
See that CI is passing

## DevOps Notes
<!-- Please uncheck these items as applicable to make DevOps aware of changes that may affect releases -->
- [x] This PR does not require configuration changes (e.g., environment variables, GitHub secrets, VM resources)
- [x] This PR does not affect public APIs
- [x] This PR does not rely on a new version of external services (PoET, elasticsearch, etc.)
- [x] This PR does not make changes to log messages (which monitoring infrastructure may rely on)


Co-authored-by: Bartosz Różański <bartek.roza@gmail.com>

api/grpcserver/grpc.go

@@ -71,6 +71,16 @@ func (s *Server) Start() error {
 // Close stops the server.
 func (s *Server) Close() error {
 	s.logger.Info("stopping the grpc server")
+	// GracefulStop waits for all connections to be closed before closing the
+	// server and returning. If there are long running stream connections then
+	// GracefulStop will never return. So we call it in a background thread,
+	// wait a bit and then call Stop which will forcefully close any remaining
+	// connections.
+	s.grp.Go(func() error {
+		s.GrpcServer.GracefulStop()
+		return nil
+	})
+	time.Sleep(time.Second * 1)
 	s.GrpcServer.Stop()
 	return s.grp.Wait()
 }