Format extra help page text like wiki

What does this MR do?

The instance specific help text was not rendered in any way compatible with the look and feel of the rest of the page. Just re-use the wiki style like the rest of the page.

Before

After

What are the relevant issue numbers?

#55948 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer

Closes #55948 (closed)