Installing apt packages from other sources

[Mrkol]

We want to check PRs to a project that uses vulkan with clang-tidy, but the version of Vulkan SDK provided by Ubuntu 23.04 is too old for us (yes, we like to live on the edge). Hence we need to manually install Vulkan SDK from LunarG's package server, which requires adding their public key and hooking up the apt source. Currently, this action provides no easy way to do this except for hacking in some bash lines into cmake_command, which seems to not be ideal.

It would be nice of this action provided a post-setup commands input for such use-cases.
Note that other projects have already encountered similar problems:
https://github.com/boutproject/BOUT-dev/blob/master/.github/workflows/clang-tidy-review.yml#L34

[ZedThree]

It's not perfect, but you should be able to use cmake_command to do the sorts of things you want. There's also #100, but which prove fruitful if I can find the time