Pick AI provider for each feature

As plotly studio becomes configured to offer many different AI experiences, we can allow users to customize which AI providers and models they'd like to use for different requests. This can be helpful when trying to optimize for costs or security. We should offer strong out of the box defaults for users here, but let them ultimately select this for themselves centrally. By making this a central configuration setting, we can minimize the need to offer settings on every AI experience in the product.

The only place where this is likely to be helpful to let the user override settings \/ experiment on their own without coming to this central page is in AI chat.