Inject data attributes to render maven dependency proxy settings

What does this MR do and why?

Inject data attributes to render maven dependency proxy settings

Also pushes packages_dependency_proxy_maven feature flag from controller

Screenshots or screen recordings

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N/A

How to set up and validate locally

Instructions

The dependency proxy for packages has a few requirements:

1. have packages -> enabled set to true in gitlab.yml.
2. have dependency_proxy -> enabled set to true in gitlab.yml.
3. have the packages feature enabled in the project's settings. Settings -> General -> Visiblity, project features, permissions -> Package registry (checkbox enabled.)
4. have a GitLab license. Premium or more.
5. Visit Project > Settings > Packages and Registries
6. Right-click and select View source, confirm data-show-dependency-proxy-settings is set to true
7. have the related feature flag turned on:

   Feature.enable(:packages_dependency_proxy_maven)

8. Confirm that gon.features.packagesDependencyProxyMaven is true from the browser console.
9. Run in FOSS mode
10. Visit Project > Settings > Packages and Registries
11. Right-click and select View source, confirm data-show-dependency-proxy-settings is set to false

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #410726 (closed)