[Identity] Implement RefreshUserPreKey

Summary:
Implement authenticated RefreshUserPreKey.

https://linear.app/comm/issue/ENG-3942

Depends on D8463

Test Plan:
Start docker, localstack, and run terraform

cd serivces/commtest
cargo test --test identity_prekey_tests

# assert prekey was changed
awslocal dynamodb scan --table-name identity-users

Reviewers: bartek, varun

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8464