MM-43084 update product limits through webhook and websocket (#20076)

* Define interfaces for updating subscriptions and product limits from CWS webhook.

plugin/api.go

@@ -1147,6 +1147,11 @@ type API interface {
 	//
 	// Minimum server version: 5.36
 	RequestTrialLicense(requesterID string, users int, termsAccepted bool, receiveEmailsAccepted bool) *model.AppError
+
+	// GetCloudLimits gets limits associated with a cloud workspace, if any
+	//
+	// Minimum server version: 7.0
+	GetCloudLimits() (*model.ProductLimits, error)
 }
 
 var handshake = plugin.HandshakeConfig{