propagate callbacks through load_summarize_chain (#7565)

This lets you pass callbacks when you create the summarize chain:

```
summarize = load_summarize_chain(llm, chain_type="map_reduce", callbacks=[my_callbacks])
summary = summarize(documents)
```
See #5572 for a similar surgical fix.

tagging @hwchase17 for callbacks work

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libs/langchain/langchain/chains/summarize/__init__.py

@@ -1,6 +1,7 @@
 """Load summarizing chains."""
 from typing import Any, Mapping, Optional, Protocol
 
+from langchain.callbacks.manager import Callbacks
 from langchain.chains.combine_documents.base import BaseCombineDocumentsChain
 from langchain.chains.combine_documents.map_reduce import MapReduceDocumentsChain
 from langchain.chains.combine_documents.reduce import ReduceDocumentsChain
@@ -49,16 +50,22 @@ def _load_map_reduce_chain(
     collapse_llm: Optional[BaseLanguageModel] = None,
     verbose: Optional[bool] = None,
     token_max: int = 3000,
+    callbacks: Callbacks = None,
     **kwargs: Any,
 ) -> MapReduceDocumentsChain:
-    map_chain = LLMChain(llm=llm, prompt=map_prompt, verbose=verbose)
+    map_chain = LLMChain(
+        llm=llm, prompt=map_prompt, verbose=verbose, callbacks=callbacks
+    )
     _reduce_llm = reduce_llm or llm
-    reduce_chain = LLMChain(llm=_reduce_llm, prompt=combine_prompt, verbose=verbose)
+    reduce_chain = LLMChain(
+        llm=_reduce_llm, prompt=combine_prompt, verbose=verbose, callbacks=callbacks
+    )
     # TODO: document prompt
     combine_documents_chain = StuffDocumentsChain(
         llm_chain=reduce_chain,
         document_variable_name=combine_document_variable_name,
         verbose=verbose,
+        callbacks=callbacks,
     )
     if collapse_prompt is None:
         collapse_chain = None
@@ -74,6 +81,7 @@ def _load_map_reduce_chain(
                 llm=_collapse_llm,
                 prompt=collapse_prompt,
                 verbose=verbose,
+                callbacks=callbacks,
             ),
             document_variable_name=combine_document_variable_name,
         )
@@ -82,12 +90,14 @@ def _load_map_reduce_chain(
         collapse_documents_chain=collapse_chain,
         token_max=token_max,
         verbose=verbose,
+        callbacks=callbacks,
     )
     return MapReduceDocumentsChain(
         llm_chain=map_chain,
         reduce_documents_chain=reduce_documents_chain,
         document_variable_name=map_reduce_document_variable_name,
         verbose=verbose,
+        callbacks=callbacks,
         **kwargs,
     )