Draft: Add a GraphQL mutation to update group members role in bulk

What does this MR do and why?

Add a mutation to change max role of direct members in a group in bulk

Sample mutation and output

Mutation

mutation {
  groupMembersUpdate(input: {
    groupId: "gid://gitlab/Group/264"
    accessLevel: 20
    expiresAt: "2022-06-08 08:00:00"
    groupMemberIds: [
      "gid://gitlab/GroupMember/194",
    ]
  }) {
    groupMembers {
      id
      accessLevel {
        integerValue
        stringValue
      }
    }
  }
}

Output

{
  "data": {
    "groupMembersUpdate": {
      "groupMembers": [
        {
          "id": "gid://gitlab/GroupMember/194",
          "accessLevel": {
            "integerValue": 20,
            "stringValue": "REPORTER"
          }
        }
      ]
    }
  }
}

How to set up and validate locally

1. Open http://localhost:3000/-/graphql-explorer.
2. Run the above mutation for multiple users and check that the role of the group members change.

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.

Related to #354749 (closed)