Set up CI with Github actions

[cristiano-belloni]

I set up a simple test CI in https://github.com/zambezi/caballo-vivo/tree/actions-ci, but it says Actions is not available for legacy per-repository billing plans. Please visit your billing settings to upgrade your account (failed build is here).

AFAIK, Github Actions are free - maybe it's just a simple switch to flip, @mstade ?

[mstade]

Looks like it should be included but there's something funky about our organization subscription plan, looks like maybe it's bugged out somehow. GitHub actions should be included (up to 2000 min) but then it also says the allowance will reset in -800 days or something, which obviously looks off. I'd say get in touch with GitHub support and ask them to take a look at it, I don't think there's much I can do unfortunately. :o(