Update Dockerfile and PHP 7.4 Configs for XDebug with local dev

[llslim]

Copy PHP config files at the top of dockerfile for scripts like pear/pecl can be configured to do things like add extensions automatically.

I applied this sane configuration for php.ini and php-fpm configs from devilbox after weeks/months of getting 504 gateway errors. Reference to devilbox issue: cytopia/devilbox#234 (comment)

Setting max_execution_time in php.ini, and set request_terminate_time to 300 seconds for xdebug.

Re-organize files for better clarity.