Add hires upscale, add variation parameter

[hollowstrawberry]

• Implemented hires fix (upscale), in the form of a button that opens an ephemeral interactive message, letting you select some settings before upscaling the image. The image is made from scratch with the same parameters, but this time with "hires fix" mode at the end, which increases its size and quality. This button is not present with images larger than 768x768 pixels.
• The new variation parameter lets you finetune details within the same seed. Regenerating an image that has a variation value above 0 will use the same seed but change the subseed instead.
• The code was slightly cleaned up, with a couple extra checks for stability.
• The slash command parameter descriptions were again tweaked to be more informative.
• The default negative prompt was changed to a more modern and minimalist approach. It should be very effective on recent anime checkpoints (last 6 months) among others.

[zhaobenny]

using git trying to fix a typo be like