Add awardEmoji field to more graphql types

What does this MR do and why?

This field is already available for epics. But it is also possible to add award emojis to merge requests.
This MR makes the information available via the GraphQL API.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

Visit https://127.0.0.1:3000/-/graphql-explorer

This query should do it:

query mrAwardEmojis {
  project(fullPath: "gitlab-org/gitlab-test") {
    mergeRequests {
      nodes {
        awardEmoji {
          nodes {
            name
            user {
              username
            }
          }
        }
      }
    }
  }
}

Some merge requests should have a non-empty array for awardEmoji. If all are empty, you might need to manually add some award emojis to merge requests.

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.