Adds support for updating maven dependency proxy settings

What does this MR do and why?

Adds support for updating maven dependency proxy settings

Adds submit button

Splits form into separate component

Calls mutation when maven form is submitted

This MR is follow-up to Calls mutation when dependency proxy packages s... (!139379 - merged)

Screenshots or screen recordings

Demo:

Screen_Recording_2023-12-13_at_1.08.31_am

How to set up and validate locally

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. have the related feature flag turned on:

   Feature.enable(:packages_dependency_proxy_maven)

6. Visit Project > Settings > Packages and Registries

7. Under the Dependency Proxy settings block, try updating the Maven form

8. Ensure the following:

   1. Submit button is visible & gets disabled when submitting.
   2. Submitting the form shows a toast when successful.
   3. Submitting the form shows error alert with correct message when request fails.
   4. Toggling the toggle does not change form state.

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.

Closes #410726 (closed)