feat(docs): Add migrating memory docs (#6873)

docs/core_docs/.gitignore

@@ -138,6 +138,8 @@ docs/how_to/multimodal_inputs.md
 docs/how_to/multimodal_inputs.mdx
 docs/how_to/migrate_agent.md
 docs/how_to/migrate_agent.mdx
+docs/how_to/message_history.md
+docs/how_to/message_history.mdx
 docs/how_to/merge_message_runs.md
 docs/how_to/merge_message_runs.mdx
 docs/how_to/logprobs.md
@@ -198,14 +200,14 @@ docs/how_to/character_text_splitter.md
 docs/how_to/character_text_splitter.mdx
 docs/how_to/cancel_execution.md
 docs/how_to/cancel_execution.mdx
+docs/how_to/callbacks_serverless.md
+docs/how_to/callbacks_serverless.mdx
 docs/how_to/callbacks_runtime.md
 docs/how_to/callbacks_runtime.mdx
 docs/how_to/callbacks_custom_events.md
 docs/how_to/callbacks_custom_events.mdx
 docs/how_to/callbacks_constructor.md
 docs/how_to/callbacks_constructor.mdx
-docs/how_to/callbacks_backgrounding.md
-docs/how_to/callbacks_backgrounding.mdx
 docs/how_to/callbacks_attach.md
 docs/how_to/callbacks_attach.mdx
 docs/how_to/binding.md
@@ -214,6 +216,12 @@ docs/how_to/assign.md
 docs/how_to/assign.mdx
 docs/how_to/agent_executor.md
 docs/how_to/agent_executor.mdx
+docs/versions/migrating_memory/conversation_summary_memory.md
+docs/versions/migrating_memory/conversation_summary_memory.mdx
+docs/versions/migrating_memory/conversation_buffer_window_memory.md
+docs/versions/migrating_memory/conversation_buffer_window_memory.mdx
+docs/versions/migrating_memory/chat_history.md
+docs/versions/migrating_memory/chat_history.mdx
 docs/integrations/vectorstores/weaviate.md
 docs/integrations/vectorstores/weaviate.mdx
 docs/integrations/vectorstores/upstash.md
@@ -252,10 +260,6 @@ docs/integrations/toolkits/sql.md
 docs/integrations/toolkits/sql.mdx
 docs/integrations/toolkits/openapi.md
 docs/integrations/toolkits/openapi.mdx
-docs/integrations/stores/in_memory.md
-docs/integrations/stores/in_memory.mdx
-docs/integrations/stores/file_system.md
-docs/integrations/stores/file_system.mdx
 docs/integrations/text_embedding/togetherai.md
 docs/integrations/text_embedding/togetherai.mdx
 docs/integrations/text_embedding/openai.md
@@ -278,12 +282,18 @@ docs/integrations/text_embedding/bedrock.md
 docs/integrations/text_embedding/bedrock.mdx
 docs/integrations/text_embedding/azure_openai.md
 docs/integrations/text_embedding/azure_openai.mdx
+docs/integrations/stores/in_memory.md
+docs/integrations/stores/in_memory.mdx
+docs/integrations/stores/file_system.md
+docs/integrations/stores/file_system.mdx
 docs/integrations/retrievers/tavily.md
 docs/integrations/retrievers/tavily.mdx
 docs/integrations/retrievers/kendra-retriever.md
 docs/integrations/retrievers/kendra-retriever.mdx
 docs/integrations/retrievers/exa.md
 docs/integrations/retrievers/exa.mdx
+docs/integrations/retrievers/bm25.md
+docs/integrations/retrievers/bm25.mdx
 docs/integrations/retrievers/bedrock-knowledge-bases.md
 docs/integrations/retrievers/bedrock-knowledge-bases.mdx
 docs/integrations/llms/together.md
@@ -304,10 +314,10 @@ docs/integrations/llms/cloudflare_workersai.md
 docs/integrations/llms/cloudflare_workersai.mdx
 docs/integrations/llms/bedrock.md
 docs/integrations/llms/bedrock.mdx
-docs/integrations/llms/arcjet.md
-docs/integrations/llms/arcjet.mdx
 docs/integrations/llms/azure.md
 docs/integrations/llms/azure.mdx
+docs/integrations/llms/arcjet.md
+docs/integrations/llms/arcjet.mdx
 docs/integrations/chat/togetherai.md
 docs/integrations/chat/togetherai.mdx
 docs/integrations/chat/openai.md
@@ -332,10 +342,10 @@ docs/integrations/chat/bedrock_converse.md
 docs/integrations/chat/bedrock_converse.mdx
 docs/integrations/chat/bedrock.md
 docs/integrations/chat/bedrock.mdx
-docs/integrations/chat/arcjet.md
-docs/integrations/chat/arcjet.mdx
 docs/integrations/chat/azure.md
 docs/integrations/chat/azure.mdx
+docs/integrations/chat/arcjet.md
+docs/integrations/chat/arcjet.mdx
 docs/integrations/chat/anthropic.md
 docs/integrations/chat/anthropic.mdx
 docs/integrations/retrievers/self_query/weaviate.md
@@ -375,4 +385,4 @@ docs/integrations/document_loaders/file_loaders/pdf.mdx
 docs/integrations/document_loaders/file_loaders/directory.md
 docs/integrations/document_loaders/file_loaders/directory.mdx
 docs/integrations/document_loaders/file_loaders/csv.md
-docs/integrations/document_loaders/file_loaders/csv.mdx
+docs/integrations/document_loaders/file_loaders/csv.mdx