Add xdebug3 support as separate image type

[Den4ik]

Description
This PR provide support of xdebug3 as separate images that can be configured in .env file by PHP_XDEBUG_3=1 directive

Related Issue
#267

[ihor-sviziev]

@davidalger could you check it?

[davidalger]

Looks really good. I'm going to build these and give it a run. Since it's opt-in, I'm not too concerned with it breaking anyone's workflows. Good call on adding a feature flag for it. Perhaps sometime it can be removed and this go Xdebug 3 by default once it's stable and accepted by many.

As Xdebug 3 is only available for PHP 7.2+ the image build tooling will need to be updated to only build the xdebug3 variant for 7.2 and higher. I'm working on addressing this now It'd_ be simpler if the images were simply updated to install xdebug3 when php version supports it, but that would require everyone start using it right away, which we don't want here for now.

[davidalger]

Updated the build script so it should pass muster when this is merged (not attempting to build xdebug3 images on older versions of PHP) and then ran this on a local builder:

export PHP_VERSION=7.4 \
  && ./images/scripts/build.sh --push php-fpm/xdebug3 \
  && ./images/scripts/build.sh --push php-fpm/magento1/xdebug3 \
  && ./images/scripts/build.sh --push php-fpm/magento2/xdebug3

The following images are now available on docker hub so this can be tested:

wardenenv/php-fpm:7.4-xdebug3
wardenenv/php-fpm:7.4-magento1-xdebug3
wardenenv/php-fpm:7.4-magento2-xdebug3

Once merged the rest should build via CI.

[davidalger]

Spun up a 2.4.2 sandbox running PHP 7.4, verified requests work and would stop on a breakpoint with and without PHP_XDEBUG_3=1 using VSCode on ports 9000 (Xdebug 2) and 9003 (Xdebug 3) with success in both cases. Going to merge this, and hopefully tag a release sometime this week. Thanks!