Expose agent authorizations in GraphQL

NOTE: This MR is based on Persist user_access Agent Authorizations (!116363 - closed)

What does this MR do and why?

This MR introduces GraphQL query to expose Clusters::AgentAuthoriztion model for Show shared agents in deployment projects (#395498 - closed).

Screenshots or screen recordings

Query:

query {
  project(fullPath: "root/agent-ci-test") {
    clusterAgentAuthorizations {
      nodes {
        agent {
          id
          project {
            name
          }
        }
        config
        type
      }
    }
  }
}

Response:

{
  "data": {
    "project": {
      "clusterAgentAuthorizations": {
        "nodes": [
          {
            "agent": {
              "id": "gid://gitlab/Clusters::Agent/37",
              "project": {
                "name": "agent-ci-test"
              }
            },
            "config": {},
            "type": "Clusters::Agents::ProjectAuthorization"
          },
          {
            "agent": {
              "id": "gid://gitlab/Clusters::Agent/43",
              "project": {
                "name": "agent-ci-test-2"
              }
            },
            "config": {},
            "type": "Clusters::Agents::ProjectAuthorization"
          }
        ]
      }
    }
  }
}

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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