Improve help pages with documentation

What does this MR do?

To make documentation rendered under GitLab UI more readable

• Limit width container
• Increase font-size to 110%

For #33349 (closed) until &693 (closed) is done

Screenshots

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Style guides
• Separation of EE specific content