Add image for PHP 8

[wmortada]

Now that CiviCRM officially supports PHP 8, I think we should add an image that runs PHP 8 to this repository.

[michaelmcandrew]

Yes - agreed. See https://lab.3sd.io/tools/civicrm-buildkit-docker/-/commit/d6686f5b5a09981ea6443bfe75c2cfbfd997ce8c. Just seeing what happens / if it will actually build...

[wmortada]

Just tested this locally and it works for me.

I'm getting a warning for the blank line in the Dockerfile though. This line should be deleted: publish/templates/civicrm/Dockerfile.twig#L62

vim \
  zip \
# Delete me!
  && rm -r /var/lib/apt/lists/*