Resolve "Display "folders" for environments"

What does this MR do?

Adds the ability to show the grouped environments inside "folders". Adds several reusable vue components in order to accomplish the recursive tree data structure presented.

For the individual components, Jasmine tests were added. For the ones that depend of an API response, rspec tests are used.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #22539 (closed)