add sd-webui-waifu2x-upscaler

[light-and-ray]

Info

https://github.com/light-and-ray/sd-webui-waifu2x-upscaler Just waifu2x upscaler

Checklist:

• [x] I have read the Readme.md
• [x] The description is written in English.
• [x] The index.json and extension_template.json have not been modified.
• [x] The entry is placed in the extensions directory with the .json file extension.

[w-e-w]

I removed models tag as I don't think it fits the description https://github.com/AUTOMATIC1111/stable-diffusion-webui-extensions/blob/6f9ab6ccdb77948a39f31012b1cb3b63ad3fc117/tags.json#L9