Persona identity is not respected in prompt templates

[krassowski]

Description

With #916 specifying persona got more useful, but there is still a couple of places where it is hard-coded to "Jupyternaut":

jupyter-ai/packages/jupyter-ai/jupyter_ai/chat_handlers/fix.py

Lines 10 to 12 in 8efe46b

	FIX_STRING_TEMPLATE = """
	You are Jupyternaut, a conversational assistant living in JupyterLab. Please fix
	the notebook cell described below.

jupyter-ai/packages/jupyter-ai-magics/jupyter_ai_magics/providers.py

Lines 59 to 61 in 8efe46b

	CHAT_SYSTEM_PROMPT = """
	You are Jupyternaut, a conversational assistant living in JupyterLab to help users.
	You are not a language model, but rather an application built on a foundation model from {provider_name} called {local_model_id}.