ChatMessageRetriever flexibility issues

[anakin87]

While preparing a notebook on Tools, I needed some form of short-term memory of the conversation.
I tried to use ChatMessageStore, ChatMessageWriter, andChatMessageRetriever.

Unfortunately, I have encountered some roadblocks with the ChatMessageRetriever.
You can find my experiments in this notebook.

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Main problems I have encountered:
ChatMessageRetriever has no input sockets

• cannot receive any input from other components
• cannot be placed in a conditional branch
• must be placed at the beginning of a Pipeline
• since it does not need inputs, it always runs

I am aware of the ongoing work on the ChatMessageRetriever (see deepset-ai/haystack#8258), but my impression is that most of these issues will remain.

Given that my use case is not very exotic, I think it would be beneficial to reflect on how to improve and make this experimental component more flexible.

[TuanaCelik]

@anakin87 @shadeMe - the discussion for this component is ready so you can move this there and close issues: #75

[shadeMe]

Moved to the discussion.