Release the beta of the Maven Virtual Registry

🌴 Context

The Maven virtual registry is a feature that is in beta. It has been implemented across several MRs and as such a beta feature flag has been used.

We reached a point where the beta users are happy with the current state and we would like to let other users (in particular, self-managed and dedicated) to try the feature.

To achieve that, we rolled out the flag on gitlab.com and it has been enabled for a day.

With this MR, we enable the flag by default so that self-managed and dedicated setups will have access to the feature.

We choose to use a default enabled feature flag. This way, in case of an issue, we or self-managed admins can quickly disable the feature as we don't have a general toggle for it.

🤔 What does this MR do and why?

• Enable maven_virtual_registry by default.
• Update the related docs.

📚 References

• [Feature flag] Enable maven_virtual_registry (#542415) • David Fernandez, Moaz Khalifa • 19.5 • At risk
• https://docs.gitlab.com/user/packages/virtual_registry/maven/

🦄 Screenshots or screen recordings

No UI changes.

⚙️ How to set up and validate locally

Follow https://docs.gitlab.com/user/packages/virtual_registry/maven/ to set up a virtual registry and pull a file.

🏁 MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

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