Make the default chat window memory size configurable

[michaelchia]

Problem

Chat conversation memory window of 2 is a bit small especially as people are used to long memories from their experiences with ChatGPT.

Proposed Solution

• Make the k param in the ConversationBufferWindowMemory of the DefaultChatHandler configurable.
• Preferably as a setting in the UI.
• But short-term fix of setting as some global constant like MEMORY_K = 2 which I am able to configure would be fine in the meantime.
• Can consider as provider-level configuration with provider-level default if differing context windows sizes are an issue.

Additional context

[dlqqq]

@michaelchia Yes, agreed. We set that limit earlier in 0.x because a lot of users were running into token limit issues. We're working on two different tasks in parallel:

1. A more robust configuration system
2. A better strategy for tracking token usage and limiting prompt size

I will make your issue a priority for when I implement the configuration system.

[JasonWeill]

Related to #218, a major config refactor.

[dlqqq]

This issue was fixed long ago, but we forgot to close this issue. Users can now use --AiExtension.default_max_chat_history=... to set the number of historical messages passed to the chat model. 🎉