Support two new filters, only and foldersOnlyAfterFilter

[cmaster11]

The new filters are:

• only: the opposite of ignore
• foldersOnlyAfterFilter: get the list of changed folders only after having applied the include/only filters

Copying from the readme, the example is:

Example: multi-project repo

One possible usage of this action is when you have a repository containing multiple subprojects and you want
to build each folder only when a file in that folder changes, let's say a VERSION file.

.github/
proj1/
  main.js
  VERSION
proj2/
  main.js
  VERSION
proj3/
  main.js
  VERSION
readme.md

Given an example action defined like

- uses: Stockopedia/action-get-changed-files@v1
  id: get_changed
  with:
    github-token: ${{ secrets.GITHUB_TOKEN }}
    # Only find folders containing a VERSION file that has changed
    only: "*/VERSION"
    # Get the changed folders names, but only after having applied the `only` filter
    foldersOnlyAfterFilter: true 
    format: csv
- name: Echo changed files
  run: echo ${{ steps.get_changed.outputs.changed }}

And you change the VERSION file in the proj1 and proj2 folders, the result of echo ${{ steps.get_changed.outputs.changed }} above would be

proj1, proj2