[Example] Embeddable by Reference and Value (#68719)

Added an attribute service to embeddable start contract which provides a higher level abstraction for embeddables that can be by reference OR by value. Added an example that uses this service.

examples/embeddable_examples/server/book_saved_object.ts

@@ -0,0 +1,40 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { SavedObjectsType } from 'kibana/server';
+
+export const bookSavedObject: SavedObjectsType = {
+  name: 'book',
+  hidden: false,
+  namespaceType: 'agnostic',
+  mappings: {
+    properties: {
+      title: {
+        type: 'keyword',
+      },
+      author: {
+        type: 'keyword',
+      },
+      readIt: {
+        type: 'boolean',
+      },
+    },
+  },
+  migrations: {},
+};

examples/embeddable_examples/server/plugin.ts

@@ -19,10 +19,12 @@
 
 import { Plugin, CoreSetup, CoreStart } from 'kibana/server';
 import { todoSavedObject } from './todo_saved_object';
+import { bookSavedObject } from './book_saved_object';
 
 export class EmbeddableExamplesPlugin implements Plugin {
   public setup(core: CoreSetup) {
     core.savedObjects.registerType(todoSavedObject);
+    core.savedObjects.registerType(bookSavedObject);
   }
 
   public start(core: CoreStart) {}