[web] hook to get device key upload data

Summary: this diff introduces a hook that will be passed to IdentityServiceClientWrapper. this hook will let us get the data required for DeviceKeyUpload when the login methods are called.

Test Plan: tested in next diff

Reviewers: ashoat, kamil, tomek

Reviewed By: ashoat, kamil

Subscribers: michal

Differential Revision: https://phab.comm.dev/D10808