fix(document_loaders/telegram): fix pandas calls + add tests (#4806)

# Fix Telegram API loader + add tests.
I was testing this integration and it was broken with next error:
```python
message_threads = loader._get_message_threads(df)
KeyError: False
```
Also, this particular loader didn't have any tests / related group in
poetry, so I added those as well.

@hwchase17 / @eyurtsev please take a look on this fix PR.

---------

Co-authored-by: Dev 2049 <dev.dev2049@gmail.com>

docs/modules/indexes/document_loaders/examples/telegram.ipynb

@@ -59,9 +59,11 @@
    "id": "3e64cac2",
    "metadata": {},
    "source": [
-    "`TelegramChatApiLoader` loads data directly from any specified channel from Telegram. In order to export the data, you will need to authenticate your Telegram account. \n",
+    "`TelegramChatApiLoader` loads data directly from any specified chat from Telegram. In order to export the data, you will need to authenticate your Telegram account. \n",
     "\n",
     "You can get the API_HASH and API_ID from https://my.telegram.org/auth?to=apps\n",
+    "\n",
+    "chat_entity – recommended to be the [entity](https://docs.telethon.dev/en/stable/concepts/entities.html?highlight=Entity#what-is-an-entity) of a channel.\n",
     "\n"
    ]
   },
@@ -72,10 +74,12 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "loader = TelegramChatApiLoader(user_name =\"\"\\\n",
-    "                            chat_url=\"<CHAT_URL>\",\\\n",
-    "                            api_hash=\"<API HASH>\",\\\n",
-    "                        api_id=\"<API_ID>\")"
+    "loader = TelegramChatApiLoader(\n",
+    "    chat_entity=\"<CHAT_URL>\", # recommended to use Entity here\n",
+    "    api_hash=\"<API HASH >\", \n",
+    "    api_id=\"<API_ID>\", \n",
+    "    user_name =\"\", # needed only for caching the session.\n",
+    ")"
    ]
   },
   {
@@ -113,10 +117,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-
    "version": "3.9.13"
-
-
   }
  },
  "nbformat": 4,