Add code for building a search index over added/modified entities

This is not actually being inserted yet, because doing so needs a little refactoring of the database code that happens in another PR.

Adding separate PR for the index to make it easier to review the logic.

plugins/catalog-backend/src/database/Database.ts

@@ -27,6 +27,7 @@ import {
   DbEntityResponse,
   DbLocationsRow,
 } from './types';
+import { buildEntitySearch } from './search';
 
 function serializeMetadata(
   metadata: DescriptorEnvelope['metadata'],