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/app.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/mattermost/mattermost-server/v6/einterfaces"
 	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/v6/product"
 	"github.com/mattermost/mattermost-server/v6/services/httpservice"
 	"github.com/mattermost/mattermost-server/v6/services/imageproxy"
 	"github.com/mattermost/mattermost-server/v6/services/searchengine"
@@ -174,6 +175,9 @@ func (a *App) UpdateExpiredDNDStatuses() ([]*model.Status, error) {
 	return a.Srv().Store.Status().UpdateExpiredDNDStatuses()
 }
 
+// Ensure system service adapter implements `product.SystemService`
+var _ product.SystemService = (*systemServiceAdapter)(nil)
+
 // systemServiceAdapter provides a collection of system APIs for use by products.
 type systemServiceAdapter struct {
 	server *Server