[lib/web/native] Improve conversion utils

Summary:
Improve the conversion utils situation for the future diffs:

1. Rename convertNotificationThreadIDToNewIDSchema to convertNonPendingIDToNewSchema and add idPrefix param instead of always using ashoats id
2. Add convertIDToNewSchema and use it inside convertDraftKeyToNewIDSchema

Test Plan:
yarn flow-all to test (1)
yarn jest-all to test (2) -> draft migration tests

Reviewers: kamil, inka, atul

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9147