[IMP] kwkhtmltoimage (Continuation of #31.)

[az-adhoc]

Continuation of #31.

I do not control the original head branch (ah-obs:master), so I recreated the change in this fork.

This PR continues the wkhtmltoimage support work and addresses the maintainer feedback by factoring common code and adding tests.

[sbidoul]

Thanks for working on this.

Before merging this we'll need to come up with a versioning scheme for the images we build so users can pin image tags. It's good to see contributions but we want to provide a way to pin stable versions to manage risk.

Could remove unrelated stuff from this PR (the new Dockerfile-0.12.6.2, changes to the build workflow if not necessary for this PR, unrelated README change about nektos/act, ...).

[az-adhoc]

Thanks!

You're right, I misinterpreted the development flow and added some unrelated stuff while trying to test things locally. I'll remove that and keep this PR focused.

Versioning makes sense too :-)

[az-adhoc]

@sbidoul Let me know if you want any more changes.

[sbidoul]

@az-adhoc sorry, I've not much time these days, but I'll come to it eventually.

In the meantime if you have suggestions for a tagging scheme, that would be helpful too. I will look for something that tools such as renovate can support, and I'm not quite sure how to combine the tool version with the wkhtmltopdf version. Maybe the wkhtmltopdf version must become part of the image name instead of the tag.

[az-adhoc]

@sbidoul Thanks a lot for taking the time to review this, and sorry if I sounded pushy before, that was not my intention at all 🙏
I’ve built both client and server on my fork, and I’m already running them in production successfully.

My suggestion something like:

Current style: {{version_wkhtmltox}}-latest (for example 0.12.6.1-latest)
Proposed style: {{version_wkhtmltox}}-v{{version_kwkhtmltopdf}} (for example 0.12.6.1-v1.0.0)
The idea is:

keep version_wkhtmltox to indicate the wkhtmltox base version
use SemVer for version_kwkhtmltopdf (v1.0.0, v1.1.0, etc.)

I’m also happy to commit to backward compatibility with tests, and if we ever introduce a breaking change, we bump the major version (is not the case).

If this direction sounds good to you, let me know how i can help. And please feel free to ask me directly or assign me specific tasks; I’ll gladly review them when I have a slot 🙂