Update xdebug configs for esmero-php-fpm

[aksm]

What?

Some xdebug config settings have been replaced (see here) and default ones don't need to be explicitly declared.

As a sub-issue the dev image will be built from the PHP 8 container that has the intl extension (#44) installed and enabled.

As a second sub-issue the name for the config file needs to change so it can be overridden by users deploying the container since the files are loaded in alphanumeric order. Following convention, the file will be named 10-xdebug.ini and the file shipped by deployment will be 20-xdebug.ini.