Draft: POC - Epic boards using epic work items

⚠ POC - Do not merge ⚠

What does this MR do and why?

query getEpicBoard {
  epicBoardList(id: "gid://gitlab/Boards::EpicList/3") {
    epics {
      edges {
        node {
          iid
          title
        }
      }
    }
    workItems {
      edges {
        node {
          iid
          title
        }
      }
    }
  }
}

example response

{
  "data": {
    "epicBoardList": {
      "epics": {
        "edges": [
          {
            "node": {
              "iid": "52",
              "title": "Epic 2"
            }
          },
          {
            "node": {
              "iid": "51",
              "title": "Epic 1"
            }
          }
        ]
      },
      "workItems": {
        "edges": [
          {
            "node": {
              "iid": "52",
              "title": "Epic 2"
            }
          },
          {
            "node": {
              "iid": "51",
              "title": "Epic 1"
            }
          }
        ]
      }
    }
  }
}

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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