Add compatibility with xdebug to Docker container

[e-caste]

Find a way to enable debugging through the Docker container defined in the Dockerfile.
@lvps you may want to chime in on this one to give additional details

[lvps]

@e-caste Yes: install xdebug (it's a php extension) and enable it. It should be enough... If it can connect to a server outside the container (the machine running the container, acting as a server).

Also find a way to avoid installing it at all in production

[lvps]

The container has to be split (nginx + PHP) to install xdebug, do the same thing as tarallo