Add static pre-release job

[TeofilC]

Add a job that builds a statically linked cabal-install executable, and make it available for pre-releases.

Resolves #9631.

Feedback is appreciated!
In particular, I'm not sure how we want to specify the GHC version we want for this job. I've used a singleton matrix but maybe something else is better.

I've chosen to use a standard alpine image and the haskell setup action rather than a pre-baked alpine image with GHC, since we need to install the latest version of cabal-install for the test suite anyway, and this keeps things similar to the other jobs.

[Kleidukos]

@TeofilC Thanks for this!

[ulysses4ever]

Looks cool. Have you tried it on your fork by any chance? Should suffice to merge it into master there.

[TeofilC]

Good point. I've done that now with this commit, so we can see what a merged pipeline looks like: TeofilC@831a98f

[ulysses4ever]

Looks like it works? I tried the binary (from here) on my NixOS and it looks fine.

Since you dived into the pre-release business a bit, could you also add some documentation (one paragraph could be enough but as you see fits...). How to get them is already mentioned in README, so that's covered. But I think a subsection in CONTRIBUTING.md about how they're implemented would be nice. This was mentioned on Matrix last week... Also, README has to be updated to mention the static binary.

Is it the case that we only want Linux? I personally think it's fine, but we should say something somewhere in the docs...

[TeofilC]

Sweet! I'm glad its working.

I'll write up some documentation later today. I'll take this opportunity to document the workaround from #9632 somewhere.

For the bit in CONTRIBUTING.md, I'm thinking something that gives a high level overview for how pre-releases get generated (which jobs, etc), and mention how the static one works in particular. Is that what you had in mind?

[TeofilC]

I've added a commit with some extra documentation. Let me know if that's what you had in mind @ulysses4ever or if you'd like something more/else.

Is it the case that we only want Linux? I personally think it's fine, but we should say something somewhere in the docs...

I would add non-Linux ones but I don't know how static linking works on non-linux. I've listed the configurations we have for preview releases in CONTRIBUTING.md now.

[TeofilC]

(the last force-push was just a rebase)

[ulysses4ever]

A little wordsmithing from me, but in general it's great!

[TeofilC]

I just realised I actually forgot to mention the workaround from #9632 so I've actually added that now to the README.md file 😅