Implement optional sql_mode setting

templates/etc-mysql-mysql-conf-d-mysqld.cnf

@@ -112,3 +112,8 @@ innodb_strict_mode = {{ mysql_innodb_strict_mode }}
 # ssl-ca=/etc/mysql/cacert.pem
 # ssl-cert=/etc/mysql/server-cert.pem
 # ssl-key=/etc/mysql/server-key.pem
+
+# Extras
+{% if mysql_sql_mode is defined %}
+sql_mode = "{{ mysql_sql_mode }}"
+{% endif %}