Switch composer install command from Docker to an sh script

[amatheossian1]

Create a composer_install_command.sh script, add the composer install command in it.

Check if the variable $COMPOSER_INSTALL_ARGUMENTS exists, if yes -> use it:
composer install $COMPOSER_INSTALL_ARGUMENTS
If no -> use our classic command (Remove the | true parameter on the composer command so it'll break the build in case of error)

[Buburoi]

#620