Adding support for php/pie to install php extensions

[nicosalvadore]

👉 Describe the problem

Today, the docker images are using mlocati/docker-php-extension-installer to install php extensions. Which pulls the extensions from PECL.
According to PECL website, PECL is being deprecated. A new tool called PIE is the official new way to install extensions.

👥 Problem evidence & reach

Everyone using PECL is or will be impacted sooner or later.

https://pecl.php.net/

🏆 How to solve this problem

According to the PIE docs, PIE is distributed as a PHAR, just like Composer. I would then suggest to include this package in the base docker images to allow and document the new way to install php extensions.
The current package mlocati/docker-php-extension-installer should still be in the docker images, to ensure backwards compatibility.

🥰 Describe the "impact" on users?

User would be presented with two ways to install php extensions : one legacy, and one officially supported.

Thanks in advance :)