Resolve "Error 500 due to promote group Web hooks"

What does this MR do?

It adds checks that if the promotion_link partial is used in the context of a group then it will check for it and show the links + text accordingly.

Why was this MR needed?

Because otherwise it blows up group webhooks

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #3498 (closed)