Improve UI text of group settings page - naming/visibility

What does this MR do and why?

Improves UI text of the Group > Settings page, Naming, visibility section.

Part of #350107 (closed)

• Move suffix (optional) to the field's label, to comply with https://design.gitlab.com/components/form#text
• Remov help text as it doesn't improve on any existing text.

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