Fix build errors, add ARTIFACTS_DIR and FEED_DIR, add CI

[jefferyto]

I debated whether to do so much in one PR, but I think it makes sense to group these:

• Fix the build error introduced in #9

  Since refresh can be called for any package in the repo, the entire directory needs to be writable by the Docker build user.

• Add CI

  So that the results of this PR (and future PRs) can be seen directly. I think more tests can be done, e.g. for the various build options, but I didn't want to make this more complicated that it needs to be for now. (I also chose to test with 3 architectures - in theory only one is necessary, let me know if I should add/remove any.)

• Add ARTIFACTS_DIR and FEED_DIR environment variables (action inputs)

  This is mainly to support the CI, but it is possible other workflows using this action may want to customize these. I didn't test it directly, but according to GitHub's documentation, GITHUB_WORKSPACE (and other default environment variables) cannot be overridden (which should mean other workflows cannot set a different GITHUB_WORKSPACE when calling this action).

[jefferyto]

Maybe actions need to be enabled for the repo to run the CI.

[ynezz]

Maybe actions need to be enabled for the repo to run the CI.

Indeed, this is interesting, I don't see anything which would prevent the actions from running. You're not 1st time contributor either and I don't see anything in the UI either.

[ynezz]

Should be ok now, please rebase and let's see.

[jefferyto]

@ynezz thanks!

[jefferyto]

@aparcar @ynezz any comments?

[ynezz]

@aparcar @ynezz any comments?

please rebase and let's see.

@jefferyto so can you rebase? I'm still seeing that Add CI commit of yours.

[jefferyto]

The "Add CI" commit is part of this PR, it's not in master yet.

I had already rebased earlier - you would like me to rebase again?

[jefferyto]

Oh you manually committed that commit, okay...

[jefferyto]

Rebased.

[ynezz]

tag v5.2 created

[aparcar]

Thank you both

[jefferyto]

Thanks - can update the v5 tag as well?

[aparcar]

Done