Add maven duplicates settings to package group settings

What does this MR do?

This MR adds the necessary form fields to the Packages and Registries group settings page.

note: we are using an optimistic response here, so we assume that the call to the backend will be succesful and we update the UI before the API call is successfull

This whole work is behind feature flag

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	👈 you are here!
Document + remove feature flag	TBD

Screenshots (strongly suggested)

Disabled	Enabled

Screencapture

MavenSettingsErrorHandling

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)