Monitor PECL's php-solr releases towards standard php 7.2/7.3 support

[stronk7]

In #16 we faced the problem of PECL missing a php-solr release supporting PHP 7.2. Current 2.4.0 one does not support it: https://pecl.php.net/package/solr

So, thanks to @scara we proceeded bringing support by manually compiling the extension when building the container.

This is issue is about to monitor new php-solr releases and, whenever one supporting PHP 7.2 is available... switch to it from our custom one.

Ciao :-)

[caperneoignis]

I was able to get around this in my version of 7.2 by cloning the repository directly and running the extension install. However, I did run into an issue with Oracle and a missing library SO file.