Resolve "Xdebug on macOS"

Closes #932 (closed)

What does this MR do?

This MR introduces php.ini configs dependent on the host OS for different debugging environments.

How confident are you it won't break things if deployed?

This should not change anything when deployed as only the docker-compose.dev.yml was changed and scripts/start.

Links to related issues

Debugging as a whole isn't well documented #1022.

How to test

Steps a reviewer can take to verify that this MR does what it says it does e.g.

1. Checkout branch locally
2. Start the dev environment via ./scripts/start
3. Check whether correct php.ini file is mounted depending on your host OS.

As this is deployment no tests exist

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• use "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md
• add a short text that can be used in the release notes
• Once your MR has been merged, create issue for Windows setup

Release notes text

Not necessary.