[services][backup] Scaffold gRPC server

Summary:
Created gRPC handlers, added logging and server init code. Some copy-paste from blob service.

Depends on D5842

Test Plan: Service should respond with UNIMPLEMENTED to gRPC calls.

Reviewers: varun, tomek, jon

Reviewed By: varun, tomek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D5843