Adds exclude_directories input

[alexmigf]

Currently there is not way to exclude specific directories from minification. This PR addresses this issue by adding a new input called exclude_directories which is relative to the directory input. If using more than 1 directory, they should be separated by semicolon.

Example using 1 directory

- name: Auto Minify
        uses: alexmigf/auto-minify@exclude-dirs
        with:
          directory: 'assets'
          exclude_directories: 'js/pdf_js'

Example using 2 directories

- name: Auto Minify
        uses: alexmigf/auto-minify@exclude-dirs
        with:
          directory: 'assets'
          exclude_directories: 'js/pdf_js;js/test'

[nizarmah]

Hello @alexmigf. I'm sorry for never responding to your pull request.

Thank you for putting the effort into adding this feature and documenting it.

I'll review this in the next 48 hours.