Add sd-webui-birefnet extension

[dimitribarbot]

Info

https://github.com/dimitribarbot/sd-webui-birefnet
Integrates BiRefNet background removal feature into stable-diffusion-webui.

I've also created a PR in the official stable diffusion webui rembg extension here: AUTOMATIC1111/stable-diffusion-webui-rembg#47 because I thought my extension would duplicate the existing official extension in terms of functionality.

I don't know what you prefer but we can note some differences:

• my extension adds the edge mask feature,
• my extension is using the PyTorch version of the models whereas rembg is using onnxruntime which seems to be slower (see Model Zoo section of the original author README file, under "ONNX conversion").

Checklist:

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

[w-e-w]

sorry for the delay
I was on vacation and then I became very busy (still very busy now)

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I tested the extension and it works very nicely

well ... at least the extension itself works fine
but I'm not sure there seems to be a bug webui, or something has changed about huggingface, it could also be something that I've accidentally broke on my system, I'm not sure

during testing I was not able to automatically download a model from huggingface
I'm not too sure what's the issue but I was able to fix it with a change to webui
see AUTOMATIC1111/stable-diffusion-webui#16302 (comment)

I'm asking the other developers to see if they experience of the issues or if it I broke something on my setup
if I can get a confirmation that the other people can download models using and webui is not broken then I will merge this PR immediately
but if it's not an isolated incident on my system then I prefer to postpone merging the PR
until hope when AUTOMATIC1111 comes back and start merging fixes
otherwise the people who download this extention will have trouble using it

theres some talk among a some developers that if AUTO doesn't come back soon then might carry on without Auto using a fork

thanks for your patience