Feature Request: Sync custom DB tables

### What

Custom DB tables. Or an option to select DB tables to sync.

### Why

We have custom DB tables that are not direct part of WordPress, and they are not synced, neither we have an option to select them in push and pull App screen.

### How

_No response_

Start at the push and pull App screen, then trace how WordPress database tables are discovered and selected for synchronization. Determine the existing sync entry points and how custom tables are represented. Done means users can select custom tables in the App screen and those tables sync correctly in both push and pull flows.

Written by the indexing model from the issue text.