config,backend-common: move config subscribe method to the base config interface

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/config/api-report.md

@@ -16,6 +16,9 @@ export type AppConfig = {
 //
 // @public (undocumented)
 export type Config = {
+  subscribe?(onChange: () => void): {
+    unsubscribe: () => void;
+  };
   has(key: string): boolean;
   keys(): string[];
   get<T = JsonValue>(key?: string): T;

packages/config/src/types.ts

@@ -26,6 +26,17 @@ export type AppConfig = {
 };
 
 export type Config = {
+  /**
+   * Subscribes to the configuration object in order to receive a notification
+   * whenever any value within the configuration has changed.
+   *
+   * This method is optional to implement, and consumers need to check if it is
+   * implemented before invoking it.
+   */
+  subscribe?(onChange: () => void): {
+    unsubscribe: () => void;
+  };
+
   has(key: string): boolean;
 
   keys(): string[];