Release langchain==0.2.1

langchain[patch]: Release 0.2.1 (#22074)
infra: rm unused # noqa violations (#22049)
langchain, community: move OpenAIAssistantV2Runnable to community (#22044)
langchain[patch]: remove dataclasses-json dep (#22042)
langchain: added revision_example prompt template (#20916)
OpenAI Assistants v2 api support for OpenAIAssistantRunnable (#21484)
langchain[patch]: Add unit test to detect changes to community imports (#21998)
langchain[patch]: Turn on all deprecations for 0.2 (#21999)
docs: set default anthropic model (#21988)
langchain: default to Runnable in MultiQueryRetriever (#21770)
langchain[minor]: add libs/partners to dev.Dockerfile (#21902)