Create new MysqlConnector metric exposing if the connector is tracking offsets using GTIDs or not.

Currently debezium-mysql-connector indirectly exposes if the underlying binlog client is using GTIDs to maintain its position from MySQL via the GtidSet and SourceEventPosition metrics.

Rather than indirectly infer if the connector is using Gtids by presence or absence of values in these metrics, it'd be nice if the connector directly exposed this via a metric like:

`boolean getIsGtidModeEnabled();`