[lib] Add conversions for draft store

Summary:
https://linear.app/comm/issue/ENG-3995/create-functions-for-migrating-the-client-stores
This diff introduces functions for migrating the draft store, both in cases when it is persisted in redux and when it's stored in sqlite

Depends on D8355

Test Plan: Run yarn test, tested with the next diffs if they correctly migrated the draft stores

Reviewers: kamil, tomek

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8382