Additional option --copy-original-files when outputPath is provided

[do-me]

Thanks a lot for this amazing repo!

I'm currently setting up a GitHub action based on gzipper and noticed that until now, there is no option to simply copy the original files to the (newly created) outputPath directory first. This would come in really handy for immediate deployment however.

Hence I propose --copy-original-files flag for this purpose as a possible enhancement.

If anyone needs a workaround follow these step:

1. Copy the uncompressed, original files to the compressed-branch
2. Use this branch as in- and output (in my case gh-pages)

Step 2. can be done like this:

      # check out other branch (gh-pages) 
      - uses: actions/checkout@v2
        with:
          ref: gh-pages

      # compress all files in all directories
      - run: gzipper compress --include htm,html,css,js,svg,xml,map,json,img,png,jpg,jpeg --zopfli --brotli --remove-larger .

      # commit
      - uses: stefanzweifel/git-auto-commit-action@v4
        with:
          commit_message: Compress Files
          branch: gh-pages
          push_options: '--force'

Find the full action with mkdocs deploy here.