Add mid-kdiffusion cfgdenoiser script callback - access latents, conditionings and sigmas mid-sampling

[dfaker]

Briefly discussed in the context allowing scripts to force various symmetries onto the image latents here: https://github.com/AUTOMATIC1111/stable-diffusion-webui/discussions/2441

Script with basic mirroring and rotation operation here: https://gist.github.com/dfaker/ac031e87174a94d8a170d897caac9ff6