Add Package & Registry settings menu

What does this MR do?

This MR adds a new page to the group setting to contain all the Packages & Registries settings. This is a prerequisite to implement the new Maven settings to disallow duplicated packages This work is done behind a feature flag

In this MR we are:

• Adding a new entry to the setting menu on the group sidebar
• Adding a new controller for the new page
• Adding the new route to the group routes
• Adding a new view haml file
• Bootstrapping the javascript app that will render the page
• Adding the development feature flag
• Adding a basic feature test for the new page

How to test

• open the rails console rails c
• Feature.enable(:packages_and_registries_group_settings)
• Go to a group and select settings in the sidebar

Screenshots (strongly suggested)

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)