Kafka support for QLAFilter

Original description:
Currently the QLA filter is saved to a csv file,
As a user id like the option to save the QLA filter to a table in mariadb, with a specific connection string or defaulting to the master node of monitor its attached to.

Comments:
This is likely unwise, as the amount of data could be immense (e.g. 100k QPS would cause 100k inserts/s). As Markus already suggested, a better tool is Kafka, as it's meant for storing event streams.

Resolution:
Added log_type=kafka and several Kafka-related settings to QLAFilter. Also, added setting logged_query_max_length, which limits the length of the logged query.