Fix for KeyError in MlflowCallbackHandler (#7051)

- Description: `MlflowCallbackHandler` fails with `KeyError: "['name']
not in index"`. See https://github.com/hwchase17/langchain/issues/5770
for more details. Root cause is that LangChain does not pass "name" as a
part of `serialized` argument to `on_llm_start()` callback method. The
commit where this change was made is probably this:
18af149e91.
My bug fix derives "name" from "id" field.
  - Issue: https://github.com/hwchase17/langchain/issues/5770
---------

Co-authored-by: Bagatur <baskaryan@gmail.com>

langchain/callbacks/mlflow_callback.py

@@ -551,8 +551,18 @@ class MlflowCallbackHandler(BaseMetadataCallbackHandler, BaseCallbackHandler):
         on_llm_start_records_df = pd.DataFrame(self.records["on_llm_start_records"])
         on_llm_end_records_df = pd.DataFrame(self.records["on_llm_end_records"])
 
+        llm_input_columns = ["step", "prompt"]
+        if "name" in on_llm_start_records_df.columns:
+            llm_input_columns.append("name")
+        elif "id" in on_llm_start_records_df.columns:
+            # id is llm class's full import path. For example:
+            # ["langchain", "llms", "openai", "AzureOpenAI"]
+            on_llm_start_records_df["name"] = on_llm_start_records_df["id"].apply(
+                lambda id_: id_[-1]
+            )
+            llm_input_columns.append("name")
         llm_input_prompts_df = (
-            on_llm_start_records_df[["step", "prompt", "name"]]
+            on_llm_start_records_df[llm_input_columns]
             .dropna(axis=1)
             .rename({"step": "prompt_step"}, axis=1)
         )