Bring the app end-to-end suites into this repository and retire triangle-e2e #1350

The app end-to-end suites in triangle-e2e test the hosts from builds published as releases, so a host change is only tested after it ships. Here they run against the hosts built from the same commit, next to the host-playground run from #1215.

• Decide which suites move and which stay outside
• Move the app suites onto the host-playground drivers
• Run them against hosts built from the pull request's commit
• Carry over their schedules and failure notifications
• Archive the standalone repository