[MM-28211] API pass-thru to the CWS for getting subscription (#15666)

* API pass-thru to the CWS for getting subscription

* Remove use of parameter in favour of env var

* Remove unnecessary param

* Removed unnecessary fields and added client4 method

* Some cleanup

* Translation fix

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

einterfaces/cloud.go

@@ -12,4 +12,6 @@ type CloudInterface interface {
 
 	CreateCustomerPayment() (*model.StripeSetupIntent, *model.AppError)
 	ConfirmCustomerPayment(*model.ConfirmPaymentMethodRequest) *model.AppError
+
+	GetSubscription() (*model.Subscription, *model.AppError)
 }