esmero-php: Make Xdebug faster

[marlo-longley]

What is happening?

Currently to avoid further setup by users, we have our Dockerfile.dev ship with the xdebug setting, autostart=1.
Unfortunately with this on every request, it's almost unworkably slow.
So we are trading in slightly more user setup for speed of development.
We need to turn autostart=0 and add a tiny bit more setup on the archipelago-deployment side.

See related branch in archipelago-deployment (will update this comment once we have a PR ready from this branch https://github.com/esmero/archipelago-deployment/tree/ISSUE-20)

@DiegoPino