Fix groupByNameAndOrganization resolver errors when group not found

[rocketeerbkw]

General Checklist

• Affected Issues have been mentioned in the Closing issues section
• Documentation has been written/updated
• PR title is ready for inclusion in changelog

Database Migrations

• If your PR contains a database migation, it MUST be the latest in date order alphabetically

When attempting to load a group by name and org ID, and the group either doesn't exist, or is not a part of the organization, AND the members field is requested, a cryptic error would be thrown:

{
  "errors": [
    {
      "message": "keycloakGroups is not iterable",
      "locations": [
        {
          "line": 5,
          "column": 4
        }
      ],
      "path": [
        "groupByNameAndOrganization",
        "members"
      ],
      "extensions": {
        "code": "INTERNAL_SERVER_ERROR",
        "exception": {
          "stacktrace": [
            "TypeError: keycloakGroups is not iterable",
            "    at /app/services/api/dist/models/group.js:358:37",
            "    at Generator.next (<anonymous>)",
            "    at fulfilled (/app/services/api/dist/models/group.js:28:58)",
            "    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)"
          ]
        }
      }
    }
  ],
  "data": {
    "groupByNameAndOrganization": {
      "id": null,
      "name": null,
      "members": null
    }
  }
}

This is because the resolver returns groupS but the schema expects a single group. Returning an empty array still calls the members resolver, which can't get any information for an undefined group and fails.

This PR changes the return value to be a single group, and throws a normal GroupNotFoundError.

This was broken before the keycloak upgrade refactor but the base branch is that to help with merge conflicts. Can wait to merge after keycloak upgrade.

[shreddedbacon]

@rocketeerbkw is this something that needs to be in v2.21.0?

[rocketeerbkw]

This doesn't need to hold up v2.21.0.