[web-db] migrate drafts to SQLite

Summary:
Moving drafts from redux-persist to separate table in SQLite.

Depends on D7658

Test Plan:

1. Reload app
2. Check if migration succeeded
3. Query database and check drafts content (should equals redux content)

Reviewers: tomek, michal

Reviewed By: tomek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7660