This PR restructures the integration tests and prebuilds all common assets used in all tests:
Headscale and Tailscale HEAD image
hi binary that is used to run tests
go cache is warmed up for compilation of the test
This essentially means we spend 6-10 minutes building assets before any tests starts, when that is done, all tests can just sprint through.
It looks like we are saving 3-9 minutes per test, and since we are limited to running max 20 concurrent tests across the repo, that means we had a lot of double work.
There is currently 113 checks, so we have to do five runs of 20, and the saving should be quite noticeable! I think the "worst case" saving would be 20+min and "best case" probably towards an hour.
The former is a no-op in the base images (45491f2c5c/scripts/debuerreotype-minimizing-config (L87-L109)), and `apt-get dist-clean` is a safer/better version of the `rm -rf /var/lib/apt/lists/*` that keeps the cryptographic bits that help prevent downgrade attacks.
