docs: update ApiConfig with rootNamespace

docs/en/UI/Angular/Environment.md

@@ -24,6 +24,7 @@ export interface Apis {
 
 export interface ApiConfig {
   [key: string]: string;
+  rootNamespace?: string;
   url: string;
 }
 ```
@@ -51,6 +52,8 @@ Take a look at following example
 When an api from `AbpIdentity` is called, the request will be sent to `"https://localhost:9090"`. 
 Everything else will be sent to `"https://localhost:8080"`
 
+* `rootNamespace` **(new)** : Root namespace of the related API. e.g. Acme.BookStore
+
 ## Application
 
 ```typescript