Allow prompt template customization for Jupyter AI chat.

[andrii-i]

Problem

Customizing prompt templates is at the moment only works for Jupyter AI magics and for a specific format. It's not possible to customize prompt templates for Jupyter AI chat.

Relevant issues:

• Update prompts for locally installed models #226
• Unable to use ChatVertexAI as provider due to default chat's ChatPromptTemplate #264
• Prompt template not honored for LlamaCpp mode provider #491

Relevant discussion:

• Update Users section of the docs #494 (comment)

Proposed Solution

Allow prompt template customization for Jupyter AI chat.

[cloutier]

I'm working on a use-case that would benefit greatly from this. What I would ideally want is to be able to pass my own lanchchain object as a model, were I preconfigured everything from prompt to RAG to the LLM model, all using credentials from the currently logged-in user.

This might be the simplest way implementation-wise to allow arbitrary customization.

[krassowski]

Any thoughts on the approach proposed in #581?