* MM-60705 DB migration: added update_at column to draft table for mobile
* refactor: updated docs
* refactor: reverted unwanted changes and updated default value for update_at columns
* refactor: changed the condition for excepting 0 value for update_at column
* MM-49540: drafts migration adding metadata
Adds a drafts table migration adding the column "metadata".
This column is going to be primarily used to store the draft's
metadata priority field.
* Addresses review comments