[lib] Move createAsyncMigrate to utils

Summary:
I need to split createAsyncMigrate function and after this refactoring it won't make sense for these to be in create-async-migrate.js - the new one should bo somewhere in utils. The original createAsyncMigrate should also be placed in utils probably from the beginning.

https://linear.app/comm/issue/ENG-7009/run-redux-migrations-after-the-backup-is-restored

Depends on D11947

Test Plan: Flow

Reviewers: kamil, marcin, varun

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12014