Organization overview for instance admins
## Problem
Once Organizations exist, we will need to give instance admins the ability to manage all the Organizations of their instance. We need to:
1. Decide which functionality should be available in the Organization overview (create new Organization?, delete Organization?, edit name and path?)
2. Where the Organization overview will appear
## Proposal
This Organization overview could live in the current Admin Area and provide a path into Organizations, particularly for self-managed customers to help with the transition of a lot of the current Admin Area functionality into the Organization. Designs could be heavily oriented on the existing Groups overview.

Designs - [Figma](https://www.figma.com/file/dWpaP9RjcsT3AxFr8Tih9Z/Organization-MVC-Admin?type=design&node-id=4062%3A47227&mode=design&t=one1iKMQuSa10JOm-1)
## Implementation guide
1. Add `organizations` route to [config/routes/admin.rb#L13](https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/routes/admin.rb#L13)
2. Create `app/controllers/admin/organizations_controller.rb` with an `index` action
3. Create `app/views/admin/organizations/index.html.haml`
4. Create `app/assets/javascripts/admin/organizations/index.js`
5. Move `app/assets/javascripts/organizations/index/components/organizations_list_item.vue`, `app/assets/javascripts/organizations/index/components/organizations_list.vue`, and `app/assets/javascripts/organizations/index/components/organizations_view.vue` into `app/assets/javascripts/organizations/shared/components`
6. Create `app/assets/javascripts/admin/organizations/components/app.vue` that renders `app/assets/javascripts/organizations/shared/components/organizations_view.vue`
7. Use GraphQL query added in https://gitlab.com/gitlab-org/gitlab/-/issues/431756+ for data
issue