Enable group setting to allow or prevent duplicate Maven uploads

What does this MR do?

This MR:

• Removes the feature flag
• Refactor the view files to be more consistent
• Adds docs for the new feature
• Adds missing check for package being enabled

The Plan

Feature flag rollout issue: #297371 (closed)

Step	MR
Add new page and menu entry + feature flag	!51460 (merged)
Add basic components + queries and mutations	!51883 (merged)
Wire the new UI and UX review	!52472 (merged)
Document + remove feature flag	👈 you are here!

Screenshots (strongly suggested)

No visual changes

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

Related to #296895 (closed)