Allow remote_package_files to reference a local path

[vvuk]

Describe your core improvement

The syntax for including files from a remote github repo via remote_package_files is substantially different from including local files with substitution. This makes it difficult to iterate on a config that's in the same repo as the package files locally. It would be very convenient if instead of url: ... something like path: . could be used to just point to local files.

It's possible to use url: file:///path/to/directory, but that will still do a clone -- requiring changes to be committed to the repo.

Current limitations

Users have to use very different syntax for working from local directory/repo package files vs remote

Technical benefits

Simplify local development

Additional context

No response