Disable GitLab Project Import Button if source disabled

What does this MR do?

Disables GitLab Project Import Button if "GitLab export" source is disabled in the admin dashboard

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #36882 (closed)