App for Container Registry Retention & Expiration policies

What does this MR do?

This MR adds a new panel to the settings page with a basic vue app to develop the form that will help the user configure the retention and expiration policies.

The MR is deliberately small and partial to better split an otherwise big effort in a more manageable and reviewable work.

Scope of Work / Caveats

• add a new partial to load the vuejs-app and pass props
• add feature flag to load a new html piece for the new config panel
• write down the config header in the HAML to avoid the DOM to jump around when the JS loads
• boostrap basic app
• add basic tests

Screenshots

screen-capture__14_

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

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

part of #15398 (closed)