[identity] Reduce log level for gRPC interceptors

Summary:
The auth and version interceptor logs are causes of terrible spam and it's difficult to find useful logs.
Reducing level to trace makes them distinguishable from others and allows to be disabled separately by using RUST_LOG=debug

Test Plan:
Ran identity locally and some commtest tests to make some log spam.
Tested with RUST_LOG=identity=trace vs RUST_LOG=identity=debug

Reviewers: will

Reviewed By: will

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11983