[Telemetry] Datapoints for MySQL

In scope of this ticket we have to implement next datapoints:

1. Basic MySQL Configuration. what is innodb_buffer_pool size?. Datapoint Name: mysql_global_variables_innodb_buffer_pool_size
2. Server Load. what is average threads_running during last day?. Datapoint Name: mysql_global_status_threads_running
3. Number queries per second during last day. Datapoint Name: mysql_global_status_queries_running
4. Data usage. How big is MySQL database under management? Datapoint Name: mysql_global_data_usage