[docs] Update training docs (#5512)
* first draft
* try hfoption syntax
* fix hfoption id
* add text2image
* fix tag
* feedback
* feedbacks
* add textual inversion
* DreamBooth
* lora
* controlnet
* instructpix2pix
* custom diffusion
* t2i
* separate training methods and models
* sdxl
* kandinsky
* wuerstchen
* light edits
