I've opted to leave out any additional upscaling parameters like scale
and denoising strength, which, from my review of the ESRGAN code, don't
do much:
- scale just resizes the image using CV2 after the AI upscaling, so
that's not particularly useful
- denoising strength is only valid for one class of model, which we are
no longer supporting

If there is demand, we can implement output size/scale UI and handle it
by passing the upscaled image to that a resize/scale node.

I also understand we previously had some functionality to blend the
upscaled image with the original. If that is desired, we would need to
implement that as a node that we can pass the upscaled image to.

Demo:


https://github.com/invoke-ai/InvokeAI/assets/4822129/32eee615-62a1-40ce-a183-87e7d935fbf1

---

[feat(nodes): add RealESRGAN_x2plus.pth, update upscale
nodes](https://github.com/invoke-ai/InvokeAI/commit/dbc256c5b45d1d0555989d384d4ddded88e7ca3b)

- add `RealESRGAN_x2plus.pth` model to installer @lstein 
- add `RealESRGAN_x2plus.pth` to `realesrgan` node
- rename `RealESRGAN` to `ESRGAN` in nodes
- make `scale_factor` optional in `img_scale` node

[feat(ui): restore ad-hoc
upscaling](https://github.com/invoke-ai/InvokeAI/commit/b3fd29e5ad881b8f0d381afd9498b883ba9d803e)

- remove face restoration entirely
- add dropdown for ESRGAN model select
- add ad-hoc upscaling graph and workflow