Add accessLevel & isLastOrganizationOwner fields to organizationUser

What does this MR do and why?

This is part of the ongoing organization work https://docs.gitlab.com/ee/architecture/blueprints/organization/.

We are adding these fields to the organizationUser GraphQL query so check if the current user is the last owner of the organization to see if the user can leave the organization or not.

Query plan

Raw query 1

EXPLAIN
SELECT 1 AS one
FROM "organization_users"
         INNER JOIN "users" ON "users"."id" = "organization_users"."user_id"
WHERE "organization_users"."organization_id" = 1
  AND "organization_users"."access_level" = 50
  AND ("users"."state" IN ('active'))
  AND "users"."user_type" IN (0, 6, 4, 13)
  AND "organization_users"."id" != 10000
LIMIT 1;

https://console.postgres.ai/gitlab/gitlab-production-main/sessions/27273/commands/84790

Raw query 2

EXPLAIN
SELECT 1 AS one
FROM "organization_users"
WHERE "organization_users"."organization_id" = 1
  AND "organization_users"."access_level" = 50
  AND "organization_users"."id" != 10327656
LIMIT 1;

https://console.postgres.ai/gitlab/gitlab-production-main/sessions/27273/commands/84791

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

Run the below query on https://gdk.test:3000/-/graphql-explorer:

{
  organization(id: "gid://gitlab/Organizations::Organization/1") {
    organizationUsers {
      nodes {
        id
        accessLevel {
          integerValue
          stringValue
        }
        isLastOrganizationOwner
      }
    }
  }
}

Related to #441577 (closed)