Enable way to make user an admin of an organization in web UI

[lowellrex]

#7584 added a interface for people using Caseflow to manage team membership. #7852 added a new admin field in the organizations_users table that indicates whether somebody is an admin of a given team. We should add the ability to manage admin privileges in that interface. The admin field is currently only used for determining who is the judge on a judge team, but will soon be used for other purposes (like making sure VLJ support staff admins do not get assigned tasks, and maybe managing team membership).

Acceptance criteria

• People using Caseflow should be able to make members of an team an admin of that team.

[lowellrex]

In order to allow VSO users to navigate to their queues we will:

1. Add one member of that VSO to the organization
2. Make that member an admin (using the button that will be created by this PR)
3. Allow that admin to add other folks to the VSO as they see fit