Allow to specify PHP memory_limit (128M default).

[naveenvalecha]

Allow to pass in env variable PHP_MEMORY_LIMIT with desired memory_limit.
The 128MB is the default (as it has been until now).

[marji]

I believe we could use
ARG PHP_MEMORY_LIMIT=512M instead of
ENV PHP_MEMORY_LIMIT=512M
but I guess no harm to have that variable available in the container (though it is not used for anything).
LGTM

[marji]

Actually, I have parametrised the /usr/local/etc/php/conf.d/memory-limit.ini - instead of writing in the value of the PHP_MEMORY_LIMIT variable on build time, I'm using the variable - as per https://www.php.net/manual/en/configuration.file.php

Example #1 php.ini Environment Variables

; PHP_MEMORY_LIMIT is taken from environment
memory_limit = ${PHP_MEMORY_LIMIT}

This means the 512M is the default value, but we can redefine it when creating the container, e.g.:

$ docker run --rm -ti --env PHP_MEMORY_LIMIT=256M  ghcr.io/morpht/ci-php:review-pr-16-8.2-memory /bin/bash 
ea2b06b6bf51:/$ php -i | grep memory_limit
memory_limit => 256M => 256M