Add admin organizations list view

What does this MR do and why?

Related to #419540 (closed)

The grouptenant scale team is starting to build out an Organization MVC. For more information about what an "Organization" will be see https://docs.gitlab.com/ee/architecture/blueprints/organization/

This MR adds the organizations list to the admin area. It will list all organizations in the gitlab instance. In future iterations admins will be able to delete and edit organizations.

This list view is also used in Your work -> Organizations and this MR makes the following styling adjustments to improve UX and align with group/project lists (see screenshot section):

1. Make avatar 48px on mobile and desktop (previously was 32px on mobile)
2. Make Show more/Show less button for description small
3. Add max width to description so it doesn't span the whole width of the list

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.

Screenshots or screen recordings

Desktop

Mobile

Styling changes to organizations list

Desktop

Before	After

Mobile

Before	After

How to set up and validate locally

1. Open the rails console (bin/rails console)
2. Enable the feature flag
   • Feature.enable(:ui_for_organizations)
3. (optional) create a bunch of organizations for testing

30.times do |i|
  name = FFaker::Company.name
  organization_detail = (i % 3).zero? && Organizations::OrganizationDetail.create(description: FFaker::Lorem.paragraphs.join(' '))
  Organizations::Organization.create(name: name, path: name.parameterize, organization_detail: organization_detail)
end

4. Sign in as an admin
5. Navigate to /admin/organizations