notify-feedback: Adjust event name based on notification category

Adjust the emitted feedback based on the notifaction category¹. We could
use the sound-name instead or invent x-phosh-event-name (and might even
add support for that later on) but that has the problem that the
application sometimes has a hard time to figure out what the appropriate
event is. E.g. `message-missed-instant` and `message-new-instant` are
hard to tell apart from an application PoV.

1: https://specifications.freedesktop.org/notification-spec/notification-spec-latest.html

Signed-off-by: Guido Günther <guido.gunther@puri.sm>
9 jobs for notification-event-type in 49 minutes and 1 second (queued for 3 seconds)
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