Sets the default action of this to
This action is activated when the notification is clicked on. It must be an application-wide action (it must start with "app.").
target_format is given, it is used to collect remaining positional parameters into a
Variant instance, similar to
action will be activated with that
Variant as its parameter.
When no default action is set, the application that the notification was sent on is activated.
an action name
a Variant format string, or null
positional parameters, as determined by