Is your feature request related to a problem? Please describe:
It is not obvious to users/teams when notifications are scheduled but not yet sent.

Describe the solution you'd like:
Gray/shaded log entries at the top of the alert log view showing pending messages.
Its container might have some text (e.g. info tooltip) like: "Notifications may be delayed for a particular alert if a user has received several messages recently"
The status text could be like: "pending" or "waiting to retry"

Describe alternatives you've considered:
Eventually pending messages will be logged as sent or failed.

Additional context:
These would be generated from outgoing_messages rows in the pending state, or bundled where the bundle message is in a pending state.