[Identity] Add uploadOneTimeKeys to auth service

Summary:
This endpoint should only be available to devices
which have authenticated. Also simplifies the the logic
signficantly.

https://linear.app/comm/issue/ENG-4536

Test Plan:

cd services/identity
cargo build

• Could change the identity_one_time_keys test to hit this endpoint as well

Reviewers: bartek, varun

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9059