Draft: Resolve "GraphQL API: Add `associatedProjects` field to CiRunner"

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What does this MR do and why?

References

Screenshots or screen recordings

Before	After
N/A. No such field.	New field CiRunner.associatedProjects available

How to set up and validate locally

1. Create a Project CI Runner and assign it to at least 2 projects. The first project will be its "owner project".
2. Run below query with your CI Runner ID
3. Confirm ownerProject field and associatedProjects includes the correct project, respectively.

{
  runner(id: "gid://gitlab/Ci::Runner/105") { # Change the CI Runner ID!
    ownerProject {
      name
    }
    associatedProjects(first: 100) { # NEW!
      nodes {
        name
      }
    }
    projects(first: 100) {
      nodes {
        name
      }
    }
  }
}

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Related to #378732