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:

• [x] 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.