Support download of CI-uploaded artifacts

[orevial]

It would be really helpful to be able to download artifacts uploaded during CI process.
In Gitlab the artifacts can be downloaded through /jobs/{jobId}/artifacts/download.

Example of useful command to download the artifacts of the CI build:
lab ci download
or:
lab ci artifacts

[zaquestion]

I'm into it!

[zaquestion]

Ref: https://docs.gitlab.com/ce/api/jobs.html#download-the-artifacts-archive

[zaquestion]

Thoughts:
lab ci artifacts seems like a great option for downloading the entire artifacts archive. The same syntax we use for lab ci trace should work well.

	Use:     "trace [remote [[branch]:<job>]]",

Effectively lab ci artifacts origin master:myjob

Less sure on what to do with https://docs.gitlab.com/ce/api/jobs.html#download-a-single-artifact-file -- which allows you to reach inside an archive and grab a specific file. I definitely want to support both tho!

Really just spitballin' here, the idea with branch:job was to emulate how git lets do stuff like git checkout origin branch:file -- A simple extension would just be to keep the colons going lab ci artifacts origin master:myjob:path/to/my/file, but mostly I'm wonder why colon separate at all and just do lab ci artifacts [remote [ branch [ job [ path ]]]

[jkleckner]

I found myself wanting this just today.

Something like lab ci artifacts [remote [ branch [ job [ path ]]] seems sensible.