patch: deprecate (a)get_relevant_documents (#20477)

- `.get_relevant_documents(query)` -> `.invoke(query)`
- `.get_relevant_documents(query=query)` -> `.invoke(query)`
- `.get_relevant_documents(query, callbacks=callbacks)` ->
`.invoke(query, config={"callbacks": callbacks})`
- `.get_relevant_documents(query, **kwargs)` -> `.invoke(query,
**kwargs)`

---------

Co-authored-by: Erick Friis <erick@langchain.dev>

cookbook/Multi_modal_RAG_google.ipynb

@@ -604,7 +604,7 @@
    ],
    "source": [
     "query = \"What are the EV / NTM and NTM rev growth for MongoDB, Cloudflare, and Datadog?\"\n",
-    "docs = retriever_multi_vector_img.get_relevant_documents(query, limit=1)\n",
+    "docs = retriever_multi_vector_img.invoke(query, limit=1)\n",
     "\n",
     "# We get 2 docs\n",
     "len(docs)"