ci: Move to gha

[maflcko]

Fixes #338

[achow101]

There's a snapcraft build action as well as a publish action that we may want to use instead of just doing snapcraft build in a container. Using the publish action would also let us move away from needing to use launchpad to do releases.

[maflcko]

I know there is an issue about that in #299.

My preference would be to keep this a trivial move-only for now.

Changing the build process can be done in a follow-up. Personally, I am not sure if a GHA VM is the right place to conduct a build, given that it is controlled by yet another untrusted third party, and that the VM is filled with tens of GBs of unrelated (possibly backdoored) software.

[maflcko]

The CI won't run here, because the yaml does not exist in the main branch, but the CI did run in my repo, if someone wants to take a look.

[achow101]

Can you base on main instead of 30.x? This has the 30.2 update.

[maflcko]

This is already based on main, which is missing the 30.2 update. The 30.2 update is required, because CI would otherwise fail with a hash mismatch. Unrelated: Reminds me that the curl should probably specify --fail, for an early and clearer error.

[achow101]

ACK fa2a5ef