[Keyserver] Upload new onetime keys to identity service when requested

Summary:
When receiving a "refreshKeysRequest" from tunnelbroker, keyserver
should upload new onetime keys to identity service.

https://linear.app/comm/issue/ENG-4602

Depends on D8751

Test Plan: Integration test to follow, wanted to keep this JS only

Reviewers: marcin, ashoat, jon

Reviewed By: marcin, ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8752