Add persisted selection component and fix code instruction

What does this MR do?

This MR paves the way to implement the dropdown selection to swap between Maven and Gradle in the package details page.

The new component has been added to vue_shared/components/registry because it will be re-used across all the registry types (Package, Container and Terraform)

Since for consistency we need to add this selector to all the package managers the work has been split in two

Description	MR
Add new component, fix multiline label	👈 you are here
Wire new component in all package managers	!55738 (merged)

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 MR is all background work, a changelog will be added with the next MR.
• [-] Documentation (if required)
• Code review guidelines
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• Style guides
• [-] Database guides
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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 #207467 (closed)