[lib][native] simplify and rename identity password registration hook

Summary:
renaming the hook before introducing the wallet counterpart. also simplified the logic based on feedback @tomek gave me on D10961

Depends on D11082

Test Plan: confirmed that password registration with identity service still works

Reviewers: tomek, ashoat, inka

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11083