Create detailed documentation and improve support for Xdebug

[jaydrogers]

👉 Describe the problem

Some users rely on Xdebug and there are extra steps involved to get it to work.

👥 Problem evidence & reach

• Xdebug with fpm-nginx #176

🏆 How to solve this problem

• Create documentation how to set this up in development
• Possibly make it easier by providing a standardized INI file that can easily be enabled

🥰 Describe the "impact" on users?

It will dramatically reduce the headache and effort for configuring Xdebug with PHP + Docker.

💯 How do we validate the problem is solved?

• Steps are clearly documented how to enable Xdebug
• Xdebug can easily work in development, but it does not run in production

[ps-20x]

Added a PR for spin that would add the logic described by @emilebourquin to the spin laravel basic template: serversideup/spin-template-laravel-basic#19

[afanjul]

Why only for laravel? Many users use other frameworks (yii2, symphony, etc.), so the xdebug config should be added to the base "system" for the docker in my opinion.