Add missing fields to IndexTemplate (#3129)

Co-authored-by: Quentin Pradet <quentin.pradet@elastic.co>

Author: nielsbauman

output/openapi/elasticsearch-openapi.json

@@ -64,6 +64,20 @@ export class IndexTemplate {
    * Data streams require a matching index template with a `data_stream` object.
    */
   data_stream?: IndexTemplateDataStreamConfiguration
+  /**
+   * Marks this index template as deprecated.
+   * When creating or updating a non-deprecated index template that uses deprecated components,
+   * Elasticsearch will emit a deprecation warning.
+   * @availability stack since=8.12.0
+   * @availability serverless
+   */
+  deprecated?: boolean
+  /**
+   * A list of component template names that are allowed to be absent.
+   * @availability stack since=8.7.0
+   * @availability serverless
+   */
+  ignore_missing_component_templates?: Names
 }
 
 export class IndexTemplateDataStreamConfiguration {