add generic opcache preloader for PHP 7.4 docker container

lib/preload_opcache.php

@@ -0,0 +1,42 @@
+<?php
+
+function getfiles( $path , &$files = array() ) {
+	if ( !is_dir( $path ) ) return null;
+	$handle = opendir( $path );
+	while ( false !== ( $file = readdir( $handle ) ) ) {
+		if ( $file != '.' && $file != '..' ) {
+			$path2 = $path . '/' . $file;
+			if ( is_dir( $path2 ) ) {
+				getfiles( $path2 , $files );
+			} else {
+				if ( preg_match( "/\.(php|php5)$/i" , $file ) ) {
+					$files[] = $path2;
+				}
+			}
+		}
+	}
+	return $files;
+}
+
+$preload_dirs = [
+	'application',
+	'system',
+	'modules',
+	'themes',
+];
+
+$br = (php_sapi_name() == "cli") ? "\n" : "<br />";
+$br = "\n";
+
+foreach ($preload_dirs as $dir) {
+	$files = [];
+	$full_dir = "/var/www/$dir";
+	getfiles($full_dir, $files);
+
+	echo "opcache preload ".count($files)."files from $full_dir\n";
+
+	foreach ($files as $file) {
+		echo $file.$br;
+		opcache_compile_file($file);
+	}
+}