Draft version of ubi9 image

[ViliusS]

This image is built using ubi9 base images from RedHat, and at least at some level follows s2i framework.

Pros

• It builds much faster as Apache, PHP and almost all other dependencies are already prebuilt.
• PHP is running as CGI (PHP-FPM) instead of Apache module, which in some cases could be faster.
• Various parameters from s2i framework can be used to customize Apache and PHP configuration. s2i can be used even further to build the image directly from GitHub URL + install Composer dependencies skipping ZIP download all together, though one must check if Grav is ready for that.
• Some configuration options, such as MaxRequestWorkers are automatically adjusted depending on the memory allowed during the runtime.
• Supports running Grav with HTTPS without any additional proxies. One just needs to add correct certificates to ./httpd-ssl folder.
• Image is rootless. Apache and PHP-FPM runs as default user, though this can be modified if needed by just adding USER directive to the Dockerfile.

Cons

• The image is ~20% bigger. If this is a showstopper we could try to use s2i-core base instead of s2i-base and configure Apache ourselves, as current base image includes node.js for some reason. Building from s2i-base would still be faster than previously as Apache/PHP installation in RPM OSes is straight forward.
• Doesn't include yaml PECL module as official RedHat repositories do not have it.

Caveats:

• The image removes subscription-manager so it won't ping RedHat home.
• Default port is now 8080 (8443 for HTTPS).
• Cron still runs as root, so it cannot be killed, if needed, inside rootless image.

TODO:

• Adjust default PHP settings to where they were in the old image. Most of the defaults are actually already in sync.
• Disable Apache version exposure for production use.
• Decide if a volume really should point to Grav web root. Currently I left it as it were. IMHO, it would be better to just persist /user and maybe /logs folders.
• Adjust documentation.