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/plugin.go

@@ -24,6 +24,7 @@ import (
 	"github.com/mattermost/mattermost-server/v6/app/request"
 	"github.com/mattermost/mattermost-server/v6/model"
 	"github.com/mattermost/mattermost-server/v6/plugin"
+	"github.com/mattermost/mattermost-server/v6/product"
 	"github.com/mattermost/mattermost-server/v6/services/marketplace"
 	"github.com/mattermost/mattermost-server/v6/shared/filestore"
 	"github.com/mattermost/mattermost-server/v6/shared/mlog"
@@ -38,6 +39,9 @@ type pluginSignaturePath struct {
 	signaturePath string
 }
 
+//Ensure routerService implements `product.RouterService`
+var _ product.RouterService = (*routerService)(nil)
+
 type routerService struct {
 	mu        sync.Mutex
 	routerMap map[string]*mux.Router