Update the organization endpoint to include it's members

Description

Update the /api/organizations/:id so that it includes a new attribute called members. it will be a computed property, meaning that when we retrieve the organization we'd query all the UserOrganizationGroup related to the given org_id populate a members prop. It should looks like this:

{
  ...currentOrgProps,
  members: [
    {
      group: `the UserOrganizationGroup.group`,
      user: `the UserOrganizationGroup.user`
    }
  ]
}