Add support for a custom gid.

[rjkroege]

Permit the package author to specify a custom gid by providing a
io.whalebrew.config.customgid label.

[codecov-io]

Codecov Report

Merging #64 into master will increase coverage by 0.14%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##           master      #64      +/-   ##
==========================================
+ Coverage   47.72%   47.86%   +0.14%     
==========================================
  Files          15       15              
  Lines         792      798       +6     
==========================================
+ Hits          378      382       +4     
- Misses        385      386       +1     
- Partials       29       30       +1

Impacted Files	Coverage Δ
run/docker.go	85.18% <100%> (+0.87%)	⬆️
packages/package.go	61.29% <33.33%> (-0.94%)	⬇️

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[rjkroege]

Ping: I updated this. WDYT?

[tjamet]

I was thinking about it, thought I posted the question earlier.
We already have a "keep container user" flag.
I see a single case where this could be used which is to use the current user id on the host, but keep the group id in the container, do you foresee use cases of this?

[rjkroege]

Yes. I had to add this to make a working whalebrew wrapper on MacOS for the Docker functionality of Google's gcloud tool where the gcloud in the container uses the host's Docker daemon.

[rjkroege]

Rebased.

[tjamet]

Are you using docker for Mac?
Docker for Mac has some kind of user remapping, as mounting the files in a VM, which makes that when creating and accessing files in the container, the user and group ID of the container user is used, while on the local filesystem, it is seen as the current user

Since there is now a label to keep the user ID and group an image defines LABEL io.whalebrew.config.keep_container_user 'true', I am trying to understand how specifying the group only is a distinct use case.

Can you share the package (yaml) that is not working together with the required snippets to reproduce?