Add actions to organization groups list

What does this MR do and why?

Related to #421473 (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/user/organization/

This MR continues to build the Groups and projects page by adding edit and delete actions to the groups view. Note that the Delete action doesn't actually delete the group yet. That will come in a follow-up MR when the API is ready.

What is implemented in this MR

• Add actions dropdown with edit and delete actions
• Show confirmation modal when clicking delete action

What will be implemented in future MRs

• Use real data when GraphQL API is completed - GraphQL changes for organization level group da... (#409311 - closed)
  • The mock data is hardcoded for the default GDK url. If you have a custom setup the links may not work.
• There will be some minor adjustments to the group and project list in #420800 (closed)
• Call API to delete group after confirming in modal
• Empty state
• Pagination

Screenshots or screen recordings

Desktop

Mobile

How to set up and validate locally

1. Open Rails console
   • bin/rails console
2. Enable the feature flag
   • Feature.enable(:ui_for_organizations)
3. Navigate to /-/organizations/default/groups_and_projects

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.