Customise Package list app

What does this MR do?

This MR enables the customization of the Package Registry to be able to act as an Infrastructure Registry too This work is behind feature flag and divided in several MRs:

The Plan

Description	MR
Add sidebar and pages + feature flag	!57338 (merged)
Modify package list app to be customizable	👈 you are here
Wire and customize package list app for terraform	👈 you are here
Modify package details app to be customizable	TBD
Wire and customize package details app for terraform	TBD
Final UX check, documentation and feature flag removal	TBD

Note: to move faster Modify package list app to be customizable and Wire and customize package list app for terraform have been merged in this MR, if the size of the MR grows too much we will split them again.

Screenshots (strongly suggested)

Infrastructure Registry:

List	Empty	Video
		InfraRegistry

Package Registry

List	Empty	Video
		PackageRegistry

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 all behind a feature flag.
• [-] 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 #323418 (closed)