ci: rewritten the image building action

[shanduur]

I tried to add some fixes to the CI, so the docker image is built and published (now to GHCR) correctly. This can be easily changed in the future, if GHCR does not meet the expectations.

The action should work as is, as it's mostly copy-pasted from my other project.

[CLAassistant]

All committers have signed the CLA.

[shanduur]

One more note - once the image is published in the GHCR, it is set to private by default. You will need to make it public here: https://github.com/orgs/sozu-proxy/packages/container/sozu/settings (dead link until publication)

[shanduur]

One more thing - I added Dependabot config so the dependencies might be updated automatically, but this also needs to be turned on by admins here:
https://github.com/sozu-proxy/sozu/settings/security_analysis

[shanduur]

Drafting, because even if local build works for me, the GH Action is failing, need to debug it further.

[shanduur]

Ok, passed on my repo branch, should be good for review now 🔥

[Keksoj]

This looks very nice, thank you. I have no clue wether GHCR is better than docker hub for our needs.
Would you elaborate on the relevance of GHCR as opposed to Docker Hub ?

Thoughts on Github Container Repository vs Docker hub, @FlorentinDUBOIS ?

[shanduur]

I selected it only because you do not need to manage the credentials during the build process, rotate it, etc. It's just easily integrated into the whole flow.

[Gontier-Julien]

+1 for this so i can run it on docker 💯

[FlorentinDUBOIS]

Hello, we have another pull request that fix the ci without rewriting it,
I have merged this one instead.
Besides, I am updating the credentials to be able to have the docker images available