Is your feature request related to a problem? Please describe.
The ChatMessageRetriever for RAG + Chat always provides the whole conversation history. That way, at some point the context window is exceeded.

Describe the solution you'd like
Something similar to a top_k parameter in the init of the component. That way, only a specified number of the latest chat messages is retrieved.
This could the also potentially be provided to a summary prompt node, that summarizes multiple ChatMessages.

Describe alternatives you've considered
Custom logic, where the last chat messages are stored separately and are concatenated to the query.