[docs] IP-Adapter

[stevhliu]

This (WIP) PR creates a more detailed and centralized guide for all things IP-Adapter related:

➖ removes non-loading related IP-Adapter content from the loading adapters guide
➕ adds IP-Adapter guide to the Techniques section
➕ adds set_ip_adapter_scale to the API docs
➕ IP-Adapter guide is largely divided based on tasks (text-to-image, image-to-image, image-to-video, etc.) and specific use cases (face models, instant generation, controllable generation, etc.)

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[yiyixuxu]

great! thank you
I'm not sure where to add this but I think we need to add this information here #6162 (comment)
basically for certain ip-adapter-plus checkpoints (e.g. ip-adapter-plus_sdxl_vit-h), you will have to load the image_encoder from a different folder

[sayakpaul]

This is the best guide you have written @stevhliu!

[sayakpaul]

Feel free to merge once @yiyixuxu approves. Looks really good!

[sayakpaul]

Does it make sense to indicate the file size to give an upfront idea about the tinyness of the adapter?

[stevhliu]

I think it's probably ok to not mention file size which seems like an extra detail for a reference page. It's already mentioned in the loading guide (where it is more relevant) which is linked on this page.

[khipp]

I read through the guide and added some suggestions if you don't mind. Great work!

[yiyixuxu]

thanks! feel free to merge anytime!