[lib] Reduce findUserIdentitiesActionTypes

Summary:
issue: ENG-7701
The action was added in the previous diff. Its purpose is to update existing userinfos with username and in the future - other fields

Test Plan: Tested with the rest of the stack - tested that when this action is dispatched, the entries in user store get updated with the username fetched by UserInfosHandler

Reviewers: tomek, kamil

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12218