Outline GCS deployment pathway for chat agent

We need to outline what Google Cloud infrastructure configuration and deployment we would need to do to support the chat agent feature from #2198 , including #2225 .

@vkavith and Mrunal to make a recommendation on,

* Is the announced deprecation of persistence features in LangChain a blocker to our adoption of them?
* Should we add LangGraph to our backend stack?
* Do we understand all the Google Cloud services we need to enable and configure to push the chat agent functiionality to production? (See e.g. https://docs.cloud.google.com/gemini-enterprise-agent-platform/build/runtime/quickstart )