Consider `host.docker.internal` using instead of a hardcoded IP

[basz]

Consider host.docker.internal using instead of a hardcoded IP

It looks like host.docker.internal settled as a replacement for the Mac specific version and later localhost tld and is here to stay.

[sandrokeil]

It looks like it's not working on Linux? Maybe we should remove it and should set this in via Docker env variables or we have to wait until docker/for-linux#264 was fixed?

    environment:
    - PHP_IDE_CONFIG=serverName=application
    - XDEBUG_CONFIG=remote_host=172.17.01