Add Docker Hardened Image Support

[jaydrogers]

👉 Describe the problem

• Docker made their "DHI" (Docker Hardened Images) free and open source and as of this post serversideup/php is not using them yet

👥 Problem evidence & reach

https://discord.com/channels/910287105714954251/910287106427990038/1451189005445107745

🏆 How to solve this problem

Create a version of these images that use "DHI" as a base

The official PHP DHI images are available here:

• https://hub.docker.com/hardened-images/catalog/dhi/php/images

🥰 Describe the "impact" on users?

This will greatly improve confidence in security and production use.

🤔 Things to figure out yet

• It doesn't look like zts is available (at first glance) meaning we cannot build FrankenPHP
• What about our older versions of PHP? It makes sense shipping an unsupported version of PHP is not secure so it likely will not be available. We will need to exclude these from the DHI matrix
• How should we tag these images? serversideup/php:dhi-*?

[adiologydev]

Looking forward to this.