This diff introduces the new gRPC method for the client checkpointing request to the server according to the [[ https://linear.app/comm/issue/ENG-1158#comment-a3c3f40c | ENG-1158 ashoat comment ]].
The purpose of this method is: the client sends the request to the tunnelbroker server to confirm successful checkpointing (the client successfully received and persisted the updates from the Tunnelbroker)
Related task: [[ https://linear.app/comm/issue/ENG-1158#comment-a3c3f40c | ENG-1158 ]]