events: emit event when job is deleted (#19903)

When jobs are deregistered with the `purge` flag they are immediately
deleted from the state store instead of just updated to be marked as
stopped.

Without tracking job deletions the event stream would not receive a
`JobDeregistered` event when `purge` was set.

.changelog/19903.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+api: emit `JobDeregistered` event when job is deregistered with `purge`
+```

nomad/state/events.go

@@ -125,6 +125,19 @@ func eventFromChange(change memdb.Change) (structs.Event, bool) {
 					ACLBindingRule: before,
 				},
 			}, true
+		case "jobs":
+			before, ok := change.Before.(*structs.Job)
+			if !ok {
+				return structs.Event{}, false
+			}
+			return structs.Event{
+				Topic:     structs.TopicJob,
+				Key:       before.ID,
+				Namespace: before.Namespace,
+				Payload: &structs.JobEvent{
+					Job: before,
+				},
+			}, true
 		case "nodes":
 			before, ok := change.Before.(*structs.Node)
 			if !ok {

nomad/state/events_test.go

@@ -726,7 +726,7 @@ func TestEventsFromChanges_WithDeletion(t *testing.T) {
 	event := eventsFromChanges(nil, changes)
 	require.NotNil(t, event)
 
-	require.Len(t, event.Events, 1)
+	require.Len(t, event.Events, 2)
 }
 
 func TestEventsFromChanges_WithNodeDeregistration(t *testing.T) {