Fix broken master; ensure all product service APIs have correct implementations (#20663)

* fix broken master; ensure all product service APIs are implemented by the structs passed to products

* use zero allocation interface checks

app/channels.go

@@ -312,6 +312,9 @@ func (ch *Channels) RequestTrialLicense(requesterID string, users int, termsAcce
 		receiveEmailsAccepted)
 }
 
+// Ensure hooksService implements `product.HooksService`
+var _ product.HooksService = (*hooksService)(nil)
+
 type hooksService struct {
 	ch *Channels
 }