qapi: fix example of UNPLUG_PRIMARY event

qapi: fix example of UNPLUG_PRIMARY event

Example output lacks mandatory member @timestamp.  Provide it.

Example output is not properly formatted. Fixing it by:
- Adding '<-' to signalize it is receiving the data;
- Breaking lines similar to the other examples.

Signed-off-by: Victor Toso <victortoso@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-Id: <20220328140604.41484-8-victortoso@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>