Install docker-php-extension-installer by default

[jaydrogers]

👉 Describe the problem

Adding PHP extensions is difficult because you need to know all the dependent packages.

👥 Problem evidence & reach

Anyone who wants to customize their image. For example, anyone adding Redis, PGSQL, etc.

🏆 How to solve this problem

Install docker-php-extension-installer by default

There is an open source project called docker-php-extension-installer that helps installs extensions.

• Include this in all images and install it
• Ensure all images are updated to use this new method

Document how to use this

• Show how to install common extensions
  • Redis
  • pgsql
  • imagick

🥰 Describe the "impact" on users?

• Users will have a much easier time installing extensions.
• Maintainers will answer a lot less questions on how to install extensions.

💯 How do we validate the problem is solved?

• Users can run install-php-extensions in every image variation
• Everything is clearly documented