[grpc] Using gRPC multiprocessing.

[arturgontijo]

Using the multiprocessing module with socket.SO_REUSEPORT option to spawn multiple processes to handle concurrent gRPC's requests.

Reference

[restyled-io]

Hey there-

I'm a bot, here to let you know that some code in this PR might not
match the team's automated styling. I ran the team's auto-reformatting tools on
the files changed in this PR and found some differences. Those differences can
be seen in #9.

Please see that Pull Request's description for more details.