[OSCI][FIX] Discover: Fix the Subfields Display Issue (#5429)

* set flattenHit() deep param as true to allow iterate on nested object

Signed-off-by: Qiwen Li <qiwen_li@brown.edu>

---------

Signed-off-by: qiwen li <qiwen_li@brown.edu>
Signed-off-by: Qiwen Li <qiwen_li@brown.edu>
Signed-off-by: Miki <miki@amazon.com>
Signed-off-by: Anan Zhuang <ananzh@amazon.com>
Co-authored-by: Miki <miki@amazon.com>
Co-authored-by: Anan Zhuang <ananzh@amazon.com>

CHANGELOG.md

@@ -48,6 +48,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - [Workspace] Add core workspace service module to enable the implementation of workspace features within OSD plugins ([#5092](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/5092))
 - [Workspace] Setup workspace skeleton and implement basic CRUD API ([#5075](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/5075))
 - [Decouple] Add new cross compatibility check core service which export functionality for plugins to verify if their OpenSearch plugin counterpart is installed on the cluster or has incompatible version to configure the plugin behavior([#4710](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4710))
+- [Discover] Display inner properties in the left navigation bar [#5429](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/5429)
 
 ### 🐛 Bug Fixes
 

src/plugins/data/common/index_patterns/index_patterns/flatten_hit.ts

@@ -112,7 +112,7 @@ export function flattenHitWrapper(
   metaFields = {},
   cache = new WeakMap()
 ) {
-  return function cachedFlatten(hit: Record<string, any>, deep = false) {
+  return function cachedFlatten(hit: Record<string, any>, deep = true) {
     const decorateFlattened = decorateFlattenedWrapper(hit, metaFields);
     const cached = cache.get(hit);
     const flattened = cached || flattenHit(indexPattern, hit, deep);