GraphQL project fields for refs tipping at commit

What does this MR do and why?

Build GraphQL fields for ::Type::ProjectType to be able to fetch refs tipping at a given commit

Screenshots or screen recordings

How to set up and validate locally

You can test it at http://127.0.0.1:3000/-/graphql-explorer with the following query:

query CommitParentName {
  project(fullPath: "gitlab-org/gitlab-test") {
      tagsTippingAtCommit(
        limit: 2,
        commitSha: "6f6d7e7ed97bb5f0054f2b1df789b39ca89b6ff9"
      ) {
        names
        totalCount
  		}
    
      branchesTippingAtCommit(
        limit: 2,
        commitSha: "ddd0f15ae83993f5cb66a927a28673882e99100b"
      ) {
        names
        totalCount
  		}
  }
}

Related to #325871 (closed)