[OSCI][FIX] Discover: Fix the Subfields Display Issue (#5429) (#5846)

* 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>
(cherry picked from commit 40ba1f5)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

# Conflicts:
#	CHANGELOG.md

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: opensearch-trigger-bot[bot]

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

@@ -114,7 +114,7 @@ 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);