Add XDEBUG profiler support

[maxime-claudel-totara]

Add XDEBUG profiler support.

Will need to update documentation in wiki to explain:

• to switch XDEBUG from debugger to profiler, change the environment variable in php.yml for the related php version from debugto profile. Then start the php container.
• to generate the profiler files, append &XDEBUG_TRIGGER=1 to the URL (or add cookie name XDEBUG_TRIGGER and value 1). The HTTP response header will the include X-Xdebug-Profile-Filename which contains the name of the output file.
• Profiler files are generated under /tmp/profiler-out.
• Output files can be analysed by PHPStorm (or other tools) and mapped to the source code.
• It is not recommended to keep the profiler on all the time as it slows down requests and may take up disk space.

[maxime-claudel-totara]

Needs more work to make it cleaner.