perf: index on item code for the Pick List Item doctype (backport #41357) (#41362)

* perf: index on item code for the Pick List Item doctype (#41357)

(cherry picked from commit 0887161f2a)

# Conflicts:
#	erpnext/stock/doctype/pick_list_item/pick_list_item.json

* chore: fix conflicts

---------

Co-authored-by: rohitwaghchaure <rohitw1991@gmail.com>

erpnext/stock/doctype/pick_list_item/pick_list_item.json

@@ -126,7 +126,8 @@
    "in_list_view": 1,
    "label": "Item",
    "options": "Item",
-   "reqd": 1
+   "reqd": 1,
+   "search_index": 1
   },
   {
    "fieldname": "quantity_section",
@@ -193,7 +194,7 @@
  ],
  "istable": 1,
  "links": [],
- "modified": "2023-07-25 11:56:23.361867",
+ "modified": "2024-05-07 15:32:42.905446",
  "modified_by": "Administrator",
  "module": "Stock",
  "name": "Pick List Item",
@@ -204,4 +205,4 @@
  "sort_order": "DESC",
  "states": [],
  "track_changes": 1
-}
+}