Relates #3258
After a chat with @aslushnikov we add this in two iterations. The first one (this PR) is about scheduled runs for testing the latest tip-of-tree version of the browsers daily and the next PR is about opening an automated PRs once its passing (not sure if its worth to add for failing too) or sending Telegram/Slack notifications.
Current status is that Firefox (around 2 hours) and WebKit (around 3-4 hours) works.
Known issues which I fix before we merge:
- ~~Changes in `test/base.fixture.ts` will get extracted in #3453~~
Feel free to review, current blockers are before we can merge:
- ~~#3453~~
- potential git clone optimisation by aslushnikov
