sink.text.details: show event class namespace

sink.text.details: show event class namespace

If the event class has namespace (a property introduced with MIP 1),
show it when dumping the event class info.

Example output:

    Event class `da-ec-name` (Namespace `da-ec-namespace`, ID 0):

Change-Id: Ief4363545a6379c16e229b29d8a2e0b121b4777f
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7531
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12694