Refactor directory and image location

- Removed Dockerfile for php image
+ Added php image into docker-compose file
-> Moved source for nginx/php to backend directory

Signed-off-by: Joseph Barreca <jbarrec.tech@gmail.com>

nginx-php-mysql/backend/Dockerfile

@@ -1 +0,0 @@
-FROM php:8.0.3-fpm-buster

nginx-php-mysql/backend/index.php

@@ -0,0 +1,3 @@
+<?php
+    echo '<h1>hello world in php!</h1>';
+?>