DOC-1820: Menu Toolbar Button Docs page restructuring

[LewisAtTiny]

Ticket: DOC-1820

Site: Staging branch

Changes:

• Updated Headings to differentiate how fetch works depending on search is enabled
• Update text inside the menu button example without search to explain how fetch generates a bunch of possible menu buttons
• Update text inside the searchable menu button heading to explain how the pattern variable works with fetchContext.

Pre-checks:

• Branch prefixed with feature/<version>/, hotfix/<version>/, staging/<version>/, or release/<version>/.

Review:

• Documentation Team Lead has reviewed

[kemister85]

@LewisAtTiny we need to close this PR, and create a new one based off tinymce/7 branch not main.
Branch was updated, ignore this comment.

[FarzadHayat]

@kemister85 Fixed. changed the target to tinymce/7.

[tiny-stale-bot]

This pr is stale because it has been open 365 days with no activity. Please comment if you wish to keep this pr open or it will be closed in 30 days.