Allow per-chat sampling parameters

[dvruette]

As I understand, the sampling parameters are currently stored client-side in localStorage and apply to all chats. From a user perspective, this is a bit unintuitive and it would be nice to have control over the parameters on a chat-by-chat basis. E.g. playing around with different parameters to see what gives the best results is very tedious if the settings are global.

[mtosity]

Do we have the backend support for GET/POST chat sampling parameters? I don't think using client localStorage would be efficient for this