Migrate Coverage and SAN builds to public CI

[achamayou]

We have a limited number of private executors, which we would like to free up as much as possible. Two of the four build jobs are purely virtual by necessity (SAN and coverage) and can be moved to public executors.

I tried to do that with Pipelines, but the networking restrictions they place on containers mean we cannot run the end to end tests there: #122

The best thing we can do is move them to the public CI instead and keep the private build strictly for SGX builds.