[ACA-805] extensions metadata, basic extensibility for demo shell (#3966)

* bootstrap extensibility in demo shell app

* example data

* parse and store plugin metadata

* preserve root config metadata

* show plugin info in the About box

* update tests

* update gitignore

* remove unused imports

* disable flaky test

* add missing tsconfig entries

* use pre-build project as CLI 6+ does

* update package scripts

* update tsconfig

* make dist builds work locally

* update scripts

* Revert "update scripts"

This reverts commit 58d218643fe22d642ad7f3ac67f9089ed69ec33e.

* update scripts

* use lib paths

* update configs

* update tsconfig

demo-shell/src/app/app.module.ts

@@ -68,6 +68,7 @@ import { CloudComponent } from './components/cloud/cloud.component';
 import { TaskListCloudDemoComponent } from './components/task-list-cloud-demo/task-list-cloud-demo.component';
 import { ProcessListCloudExampleComponent } from './components/cloud/process-list-cloud-example.component';
 import { TreeViewSampleComponent } from './components/tree-view/tree-view-sample.component';
+import { AppExtensionsModule } from './extensions/extensions.module';
 
 @NgModule({
     imports: [
@@ -86,7 +87,8 @@ import { TreeViewSampleComponent } from './components/tree-view/tree-view-sample
         ThemePickerModule,
         ChartsModule,
         MonacoEditorModule.forRoot(),
-        ProcessServicesCloudModule
+        ProcessServicesCloudModule,
+        AppExtensionsModule.forRoot()
     ],
     declarations: [
         AppComponent,