[web-db] create drafts table in SQLite database

Summary:
Table for storing drafts, matching native version

Depends on D7119

Test Plan: Check if table was created, e.g. console.log(sqliteDb.exec(PRAGMA table_info(drafts);));

Reviewers: michal, tomek, marcin, ashoat

Reviewed By: ashoat

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7121