added variables and default values

defaults/main.yml

 ---
-php_module_config_file: "module.ini.j2"
-php_module_priority: <module prio> 
+php_module_config_file: "mysqli.ini.j2"
+php_module_priority: 20
+php_mod_mysqli_allow_local_infile: 0
+php_mod_mysqli_local_infile_directory: ""
+php_mod_mysqli_allow_persistent: 1
+php_mod_mysqli_max_persistent: -1
+php_mod_mysqli_max_links: -1
+php_mod_mysqli_default_port: 3306
+php_mod_mysqli_reconnect: 0
+php_mod_mysqli_rollback_on_cached_plink: false

vars/Debian-10.yml

 ---
-package_packages: ["php7.3-<module>"]
+package_packages: ["php7.3-mysql"]

vars/main.yml

 ---
-php_module_name: "<module name>"
+php_module_name: "mysqli"