More customizable/customized System Prompts for different models

[cstroliadavis]

So, I've been finding that some LLMs respond better to some prompt practices than others. Having a one-size fits all approach to the system prompt might be less useful as a result, costing more money than necessary and reducing the quality of results with some LLMs over others (I find that the current system prompt is ideal for Sonnet, but some of the others have a harder time with it, unfortunately, sonnet is one of the pricier models).

It would be nice if there were options for us to be able to have more refined control over the system prompt. Perhaps there could be an advanced option that allows us to completely replace the system prompt if we choose to do so. This could be saved within a configuration profile, or perhaps we could actually link some of these with specific models if we desire (bonus).

It would be good if this prompt had the capability of still working with the other prompt parts such as role, custom instructions, mode specific instructions, etc. Perhaps by adding tokens like {{roleDefinition}}, {{customInstructions}}, etc into the custom system prompt.

Something like this might also allow devs who might have other issues with the system prompt (see #558) to more easily make those modifications themselves until such time that code updates can be made.