lttng {add,list}-triggers: use `name` instead of `id`

lttng {add,list}-triggers: use `name` instead of `id`

The right term is "trigger name", not "trigger id".  Change the option
to add-trigger accordingly, as well as the output of list-trigger.

Change-Id: I5c304aea2c37f983de001cb11c5ba8859f564617
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>