docs[patch] Add how-to doc for RunnablePassthrough and nav modificati… #10190

Job	Run time
test with unpublished langchain - Python 3.8	27s
test with unpublished langchain - Python 3.9	40s
test with unpublished langchain - Python 3.10	27s
test with unpublished langchain - Python 3.11	30s
Python 3.8 extended tests	39s
Python 3.9 extended tests	34s
Python 3.10 extended tests	46s
Python 3.11 extended tests	58s
compile-integration-tests / Python 3.8	17s
compile-integration-tests / Python 3.9	20s
compile-integration-tests / Python 3.10	23s
compile-integration-tests / Python 3.11	16s
lint / build (3.8)	32s
lint / build (3.11)	30s
test / Python 3.8	17s
test / Python 3.9	19s
test / Python 3.10	17s
test / Python 3.11	19s
	8m 31s

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