[MM-47566] Add upcominginvoice field to Subscription type (#21717)

* Add upcominginvoice field to Subscription type

* Add support for fetching upcoming invoices

* Put back upcominginvoice

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

api4/cloud.go

@@ -39,7 +39,7 @@ func (api *API) InitCloud() {
 	// GET /api/v4/cloud/subscription
 	api.BaseRoutes.Cloud.Handle("/subscription", api.APISessionRequired(getSubscription)).Methods("GET")
 	api.BaseRoutes.Cloud.Handle("/subscription/invoices", api.APISessionRequired(getInvoicesForSubscription)).Methods("GET")
-	api.BaseRoutes.Cloud.Handle("/subscription/invoices/{invoice_id:in_[A-Za-z0-9]+}/pdf", api.APISessionRequired(getSubscriptionInvoicePDF)).Methods("GET")
+	api.BaseRoutes.Cloud.Handle("/subscription/invoices/{invoice_id:[A-Za-z0-9]+}/pdf", api.APISessionRequired(getSubscriptionInvoicePDF)).Methods("GET")
 	api.BaseRoutes.Cloud.Handle("/subscription", api.APISessionRequired(changeSubscription)).Methods("PUT")
 
 	// GET /api/v4/cloud/request-trial