consider building and pushing Interop Runner Docker image in CI

[marten-seemann]

I noticed that the neqo interop runner image is now 3 years (!) old: https://hub.docker.com/r/neqoquic/neqo-qns/tags. I assume that building / pushing was done manually using this script so far.

May I suggest to push a new interop runner on every push to master, or on a daily (?) cron job? GitHub Actions has some predefined workflows that should make building and pushing Docker images pretty straightforward. For inspiration, here is quic-go's workflow, and Quinn has one as well.

[mxinden]

I am happy to contribute the required GitHub Action in case there is interest from the neqo maintainers.

[martinthomson]

@mxinden that would be great. I had a cron job setup, but I can supply the necessary secrets to get something running if you want to do the initial work. I remember having a bunch of problems with the docker hub setup at the time, so it might be easier to use the GitHub image store (I've moved to that for other projects).

[mxinden]

I prepared #1554. Let me know what you think.