Implement CI for testing nightly builds

Everyday (mostly) we build and publish nightly builds of tor and mullvad browser.

These builds are posted in https://nightlies.tbb.torproject.org/.

This ticket is about having daily test suites that run against these builds.

The objective of this test suite is to continuously make sure the main functionality of the browser is intact.

A good start to figure out what we should add to this suite is the manual QA checklist, e.g. #42755 (closed) and #43191 (closed). Also, the Onion Services QA checklist https://gitlab.torproject.org/tpo/onion-services/tor-browser-onion-qa/-/issues/4#testing. Not all of these tests make sense for a high level test suite like this one, but it's a good start.

This test suite will be run in all the supported platforms we can run it in. For now, that means x86_64 linux and android. Work is happening on tpo/tpa/team#41829 to make this platform matrix larger.