[Identity] Implement upload one time keys endpoint

Summary:
Implement upload one time keys endpoint and demonstrate with
integration test

https://linear.app/comm/issue/ENG-3943

Depends on D8126

Test Plan:

• setup localstack, run terraform locally, and start identity service

cd services/commtest && cargo test --test identity_access_tokens_tests

awslocal dynamodb scan --table-name identity-users
# should show one user having the new one-time keys

Reviewers: varun, bartek

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8127