docs: Dependency Injection guides for CLI (#19892)

PR Close #19892

aio/content/examples/dependency-injection/src/app/app-config.ts

@@ -0,0 +1,10 @@
+/*
+  Must put this interface in its own file instead of app.config.ts
+  or else TypeScript gives a (bogus) warning:
+  WARNING in ./src/app/... .ts
+  "export 'AppConfig' was not found in './app.config'
+*/
+export interface AppConfig {
+  apiEndpoint: string;
+  title: string;
+}