Disable weights auto swap with config option

[trufty]

This config option will disable the model weights from being automatically changed from the prompt's model hash key.

I often find when iterating over new dreambooth models that I want to test old prompts with new models. But when you use PNGInfo to load old prompts, it auto swaps back to my old dreambooth model, and I have to manually change back to the new one. This ends up happening a lot and I got tired of it.

Tested working with, and without, the config option selected.

This should also address https://github.com/AUTOMATIC1111/stable-diffusion-webui/issues/2831

[dfaker]

This is a good one, a minor annoyance but still a real time sink switching it back if doing cross-model work.