AI user influenced system prompt

[luke-quadratic]

Allow users and teams to create prompt templates that influence how the AI writes code in their spreadsheets.

This allows users to express preferences in how code is written, e.g. "always use xyz library for time series analysis" or "always place code cells at least two rows away from nearest content" or any other preference they may desire, becomes even more relevant as we allow the AI to do formatting, influencing formatting choices is really cool concept.

This would go in Settings under AI section as a text box.
This would be appended to system prompt.