Dependencies Group-Level: Fetch via GraphQL

What does this MR do and why?

This change adds GraphQL support for fetching dependencies at the group level, complementing the existing project-level functionality.

This is behind a new feature flag group_dependencies_graphql, which was introduced to control this functionality, which is disabled by default.

References

Screenshots or screen recordings

The rendering of the list is (apart from some missing data, which will be added in separate efforts) visually the same.

How to set up and validate locally

1. Navigate to a group-level dependency list and make sure the existing functionality (list loading, pagination, filtering, sorting, etc.) is working as expected. Note that the dependencies should be requested from the dependencies.json API.
2. Enable the related feature flag (http://gdk.test:3000/rails/features/group_dependencies_graphql) and check that now the dependencies are fetched via GraphQL and that the list is rendering as-expected. Note: Other functionality (sorting, etc.) is not yet wired up and will be done in separate efforts.

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.

Related to #527089 (closed)