add support for intermediate dependency files

[GytisBraz]

This PR adds support for intermediate dependency files. That is, files that do not exist in the project's repo but which are generated in other GitHub action steps.

• added new input FILES_EXIST
• added a couple of steps - intermediate files would be lost after the actions/checkout@v3 step (because these files do not exist in the repo that's being checked-out), so they are first moved to the $HOME dir, and then moved back from it after the checkout (this works because files inside $HOME persist between checkouts).
• updated the command python3 ./packj/main.py audit -f $input -> python3 ./main.py audit -f $input - otherwise I was getting an error /home/runner/.packj.yaml not found or something similar, which makes sense because the main.py script was being called from outside its directory but the program expects .packj.yaml in the current directory https://github.com/ossillate-inc/packj/blob/v0.15-beta/packj/main.py#L13