github-action: Allow to specify files in artefacts as input argument

[PatrickRudolph]

On Github Action files are passed between jobs using build artifacts.

Add support for directly accessing files not only in the local file system, but also in a named build artifact of a previous job, for files passed as input argument.

Files in artifacts should follow a specific syntax.
For example:

artifact://name-of-previous-build-step-artifact@/home/github/some/path/within/the/artifact