Support setting a more persistent canned (stubbed) Sampling response

[olaservo]

Is your feature request related to a problem? Please describe. Users can edit each stubbed Sampling response, this feature is to enable setting it in a more persistent way for testing using the sampling tab.

Describe the solution you'd like TODO: add more details here based on @evalstate 's suggestion.

Describe alternatives you've considered Editing the JSON for each response.

Additional context This could be a precursor to allowing for real LLM integration for testing Sampling.