Move registry settings under package_and_registries

What does this MR do?

This MR is the first step in moving all of the packages and container registry settings under the packages & registries menu and page.

In this MR we are simply moving the current code in the new folder, to have the folder structure mirror what we are already doing for group in the project too.

The Plan

Description	MR
Move existing code to new folder	👈 you are here
Gate current settings on (false) feature flag + Add a new page and controller behind feature flag + Load existing app in new page, feature tests	!59857 (merged)
Remove feature flag	TBD

Screenshots (strongly suggested)

No visual changes in this MR

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because this is a simple refactor.
• [-] 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 #297488 (closed)