Update PHP-FPM and Varnish to use Centos8 Base Images

[davidalger]

• Upstream PHP images are being updated to build atop a EL 8 vs EL 7: Add CentOS 8 images davidalger/docker-images-php#6
• IUS repositories will no longer be present in upstream base images (as of this writing they were only used to install newer versions of Git and MariaDB which were not available in EL 7 repositories)
• Git 2.27 is installed from EL 8 repositories vs Git 2.22 (git222 from IUS)
• MariaDB 10.3 client is installed from EL 8 repositories vs MariaDB 10.2 client (mariadb102 from IUS)
• The newer curl library in EL 8 will now allow constants for newer curl library features to be used in PHP code (see cURL version davidalger/docker-images-php#5 for details)

[davidalger]

Testing these has involved building the images from the upstream PR to provide EL8 base php images and then:

export PHP_VERSION=7.4
./images/scripts/build.sh php-fpm
./images/scripts/build.sh php-fpm/magento2
./images/scripts/build.sh varnish

Once the images are built locally, used a copy of this template to launch a Magneto 2 environment (without pulling during bootstrap to ensure locally built images are used):

warden bootstrap --clean-install --no-pull

After this completes, verify the application is working and operational in a browser, and verify /etc/os-release correctly report use of CentOS 8 vs CentOS 7.

[tdgroot]

LGTM, have been using this configuration for several weeks now!

[davidalger]

Now that the upstream php-fpm images are rebuilt on CentOS 8, I did a few things today to test this as well and everything appears to be A-ok.

• Rebuilt the images here on EL 8 base images: https://github.com/davidalger/docker-images-magento
• Launched an M2 Demo instance using these pre-built init images leveraging the project here: https://github.com/davidalger/m2demo/ via warden bootstrap --no-pull
• Created a from-scratch Magento 2.4 installation using my project template (https://github.com/davidalger/warden-env-magento2) and warden bootstrap --clean-install --no-pull
• Created a from-scratch Shopware 6 environment and installed with sample data successfully.

In each case I double checked I was working with EL 8 images by running warden shell and then cat /etc/os-release

Going to get this merged as soon as I can write up a change log entry and upgrade notes regarding this given it is a rather larger change.