QUA-1518: Add Computed Join History and Diff

[RafaelOsiro]

Overview

This PR adds documentation for the Query Diff feature on the Computed Join page, explaining how users can view and compare changes made to their join configurations through the History panel.

Key Changes

• Query Diff section: Added a new "Query Diff for Computed Join" section documenting the side-by-side diff view available in the History panel, including tracked fields (Select Clause, Where Clause, Group By Clause, and Join Type).
• Screenshots: Added a screenshot of the query diff dialog and updated the main Computed Join form screenshot.

Screenshots