Fix whatsappchatloader - enable parsing new datetime format on WhatsApp chat (#6555)

- Description: observed new format on WhatsApp exported chat - example:
`[2023/5/4, 16:17:13] ~ Carolina: 🥺`
  - Dependencies: no additional dependencies required
  - Tag maintainer: @rlancemartin, @eyurtsev

langchain/document_loaders/whatsapp_chat.py

@@ -29,11 +29,11 @@ class WhatsAppChatLoader(BaseLoader):
         message_line_regex = r"""
             \[?
             (
-                \d{1,2}
+                \d{1,4}
                 [\/.]
                 \d{1,2}
                 [\/.]
-                \d{2,4}
+                \d{1,4}
                 ,\s
                 \d{1,2}
                 :\d{2}

tests/integration_tests/document_loaders/test_whatsapp_chat.py

@@ -17,4 +17,5 @@ def test_whatsapp_chat_loader() -> None:
         "User 2 on 1/23/23, 3:19 AM: Bye!\n\n"
         "User 1 on 1/23/23, 3:22_AM: And let me know if anything changes\n\n"
         "~ User name 2 on 1/24/21, 12:41:03 PM: Of course!\n\n"
+        "~ User 2 on 2023/5/4, 16:13:23: See you!\n\n"
     )

tests/integration_tests/examples/whatsapp_chat.txt

@@ -2,4 +2,5 @@
 [11/8/21, 9:41:32 AM] User name: Message 123
 1/23/23, 3:19 AM - User 2: Bye!
 1/23/23, 3:22_AM - User 1: And let me know if anything changes
-[1/24/21, 12:41:03 PM] ~ User name 2: Of course!
+[1/24/21, 12:41:03 PM] ~ User name 2: Of course!
+[2023/5/4, 16:13:23] ~ User 2: See you!