Add PHP composer global installation for DevContainer

Updated composer commands to require google/cloud-storage globally and optimized autoloader during update.

This helps with https://github.com/PrivateBin/PrivateBin/issues/1641 (but technically not solve it).

.devcontainer/postCreateCommand.sh

@@ -8,8 +8,7 @@ ln -s ./conf.sample.php cfg/conf.php
 composer install --no-dev --optimize-autoloader
 
 # for PHP unit testing
-# composer require google/cloud-storage
-# composer install --optimize-autoloader
+composer require --global google/cloud-storage
 
 sudo chmod a+x "$(pwd)" && sudo rm -rf /var/www/html && sudo ln -s "$(pwd)" /var/www/html