[services][blob] Add meaningful logs in gRPC handler

Summary:
Related ENG-2308

Added log messages to the service handlers. I took advantage of spans/instruments and fields to make logs clean and structured.

Depends on D5729

Test Plan:
RUST_LOG=blob=trace cargo run and interact with the service using BloomRPC and integration tests

Example logs: https://pastebin.com/dGNkrLET

Reviewers: varun, jon, tomek, marcin, ashoat

Reviewed By: varun, jon, tomek, ashoat

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D5730