Implement ElasticSearch search engine

* Adding indexing, searching and default translator for ElasticSearch engine
* Modifying default backend to use ES if it is enabled
* Adding configuration schema to configure ElasticSearch 3 different ways
   * Elastic.co hosted solution
   * AWS hosted ElasticSearch Service
   * Custom, using standard ElasticSearch URL and auth info
* Add and modify some of the documentation regarding search

Signed-off-by: Jussi Hallila <jussi@hallila.com>

packages/backend/package.json

@@ -47,6 +47,7 @@
     "@backstage/plugin-scaffolder-backend-module-rails": "^0.1.3",
     "@backstage/plugin-search-backend": "^0.2.3",
     "@backstage/plugin-search-backend-node": "^0.4.0",
+    "@backstage/plugin-search-backend-module-elasticsearch": "^0.0.1",
     "@backstage/plugin-techdocs-backend": "^0.9.0",
     "@backstage/plugin-todo-backend": "^0.1.8",
     "@gitbeaker/node": "^30.2.0",

packages/backend/src/plugins/search.ts

@@ -22,13 +22,20 @@ import {
 import { PluginEnvironment } from '../types';
 import { DefaultCatalogCollator } from '@backstage/plugin-catalog-backend';
 import { DefaultTechDocsCollator } from '@backstage/plugin-techdocs-backend';
+import { ElasticSearchSearchEngine } from '@backstage/plugin-search-backend-module-elasticsearch';
 
 export default async function createPlugin({
   logger,
   discovery,
+  config,
 }: PluginEnvironment) {
   // Initialize a connection to a search engine.
-  const searchEngine = new LunrSearchEngine({ logger });
+  const searchEngine = config.has('search.elasticSearch')
+    ? await ElasticSearchSearchEngine.fromConfig({
+        logger,
+        config,
+      })
+    : new LunrSearchEngine({ logger });
   const indexBuilder = new IndexBuilder({ logger, searchEngine });
 
   // Collators are responsible for gathering documents known to plugins. This