Add group releases resolver and update group type

What does this MR do and why?

Resolves #360625 (closed), this MR creates a new GraphQL API endpoint for group releases. This is in preparation for migrating the Merge Request filter to use GraphQL.

Screenshots or screen recordings

How to set up and validate locally

1. Run gdk server for this branch and navigate the GraphQL explorer: http://127.0.0.1:3000/-/graphql-explorer
2. Run query for group releases, for example:

query groupReleases {
  group(fullPath: "twitter") {
    releases(sort: RELEASED_AT_DESC) {
      edges {
        node {
          name
          createdAt
          releasedAt
          description
        }
      }
    }
  }
}

3. The query should return data 😄
4. Change sort to RELEASED_AT_ASC to verify the releases sort properly

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.