Add EventCompletionAction::AckMonitorEvent

When a payment's resolution is communicated to the downstream logic via
Payment{Sent,Failed}, we may want to ack the monitor event that tells us about
the payment's resolution in the ChannelMonitor to prevent the monitor event
from being re-provided to us on startup.

Used in upcoming commits.

Author: valentinewallace

lightning/src/ln/channelmanager.rs

@@ -1613,7 +1613,14 @@ pub(crate) enum EventCompletionAction {
 	/// fully-resolved in the [`ChannelMonitor`], which we do via this action.
 	/// Note that this action will be dropped on downgrade to LDK prior to 0.2!
 	ReleasePaymentCompleteChannelMonitorUpdate(PaymentCompleteUpdate),
+
+	/// When a payment's resolution is communicated to the downstream logic via
+	/// [`Event::PaymentSent`] or [`Event::PaymentFailed`], we may want to ack the [`MonitorEvent`]
+	/// that tells us about the payment's resolution in the [`ChannelMonitor`] to prevent the monitor
+	/// event from being re-provided to us on startup.
+	AckMonitorEvent { event_source: MonitorEventSource },
 }
+
 impl_writeable_tlv_based_enum!(EventCompletionAction,
 	(0, ReleaseRAAChannelMonitorUpdate) => {
 		(0, channel_funding_outpoint, option),
@@ -1624,6 +1631,9 @@ impl_writeable_tlv_based_enum!(EventCompletionAction,
 			}
 			ChannelId::v1_from_funding_outpoint(channel_funding_outpoint.unwrap())
 		})),
+	},
+	(3, AckMonitorEvent) => {
+		(1, event_source, required),
 	}
 	{1, ReleasePaymentCompleteChannelMonitorUpdate} => (),
 );
@@ -15553,6 +15563,9 @@ impl<
 						}
 					}
 				},
+				EventCompletionAction::AckMonitorEvent { event_source } => {
+					self.chain_monitor.ack_monitor_event(event_source);
+				},
 			}
 		}
 	}