message: add instructions for how to set a custom index template
diff: @@ -102,6 +102,31 @@ import { Client } from '@elastic/elastic-search';
  const client = searchEngine.newClient(options => new Client(options));
  ```
  +#### Set custom index template
  +
  +The elasticsearch engine gives you the ability to set a custom index template if needed.
  +
  +> Index templates define settings, mappings, and aliases that can be applied automatically to new indices.
  +
  +```typescript
  +// app/backend/src/plugins/search.ts
  +const searchEngine = await ElasticSearchSearchEngine.initialize({
  + logger: env.logger,
  + config: env.config,
  +});
  +
  +searchEngine.setIndexTemplate({
  + name: '<name-of-your-custom-template>',
  + body: {
  + index_patterns: ['<your-index-pattern>'],
  + template: {
  + mappings: {},
  + settings: {},
  + },
  + },
  +});
  +```
  +
  ## Example configurations
  ### AWS
  