[Meta] Review apps

Description

Developers, Ops, Designers, PMs, and others need an easy way to see a merge request running live to properly review the request before it is deployed to production. Examples:

• Teatro
• Tutum
• Heroku Review Apps
• QEM
• Runnable

Proposal

• Creating dynamic environments: #21971 (closed)
• Destroying dynamic environments: #22191 (closed)
• Auto-close environment when branch is deleted: #23218 (closed)
• Display "folders" for environments: #22539 (closed)
• Creating Kubernetes templates: #21486 (moved)

Links

• Review apps as a GitLab Runner jobs: #20054 (closed)
• Related: #3286 (closed), #14698 (moved)