doc: zbus: improve sensor-based illustration example

The sensor-based illustration example did not consider the HLP feature
and used the work queue to publish to the Trigger channel. With the HLP,
that is not necessary anymore. The timer ISR can publish to the channel
directly. So, this commit improves the example description by
considering the HLP feature.

Signed-off-by: Rodrigo Peixoto <rodrigopex@gmail.com>