[identity] last tonic status message conversions

Summary:
Depends on D12434

there are a lot of tonic status messages that need to be converted to snake_case and dedup'd.

i've arbitrarily broken this work up into chunks to make it easier to review

this is the last diff to resolve https://linear.app/comm/issue/ENG-6477/convert-identity-service-errors-to-snake-case-and-dedup-them

Test Plan: git grep for the old status messages, change client error handling where needed

Reviewers: bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12435