Use Jetty for grpc communication

[melowe]

We need to keep an eye on this grpc issue as this would mean we could run on jetty like our other transports.

grpc/grpc-java#1621

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[melowe]

We need to check if anyone is using GRPC. Now we've added a grpc only jar perhaps it would be a better idea to leave as experimental and not to worry about this. The original issue was create to track the GPRC change.

[melowe]

Closing issue as seem more likely that GRPC will be dropped as a core option and will be left as a maintenance only or volunteer maintained module.