Need PETSc in CI for FCI

[ZedThree]

The FCI versions use the PETSc laplacian solver, so we need to ensure we have PETSc available in CI

@dschwoerer has some container based CI that include it

[mikekryjak]

@mrhardman is working on a Docker image to enable both PETSc and VANTAGE to be compiled in CI

[ZedThree]

We can also just install it via apt, that would be simplest

[dschwoerer]

I think it would be beneficial to have a pre-build image, with VANTAGE, PETSc, BOUT++, etc. That can be build once or twice, and then used repeatedly for CI.

With such an image, hermes starts compiling after around 35 seconds, and needs 2 min 42 sec to compile. In comparison the current CI in master takes also around 35 seconds to start compiling, but then takes over 5 minutes to compile. It is not a huge difference (yet), but the current CI in master has no PETSc, etc ...

Even if we install it via apt, having a pre-build image is still faster.
And on top you avoid the issue of hitting a bad mirror, and having random failure due to that.