Accept sampler designation in sampling of training

[shirayu]

• ✨ Main purpose
  • Added --ss or sample_sampler in dict to set another scheduler dynamically in training
• 🧹 Refactoring
  • Make a function get_my_scheduler() 01e00ac
  • Added a function line_to_prompt_dict() and removed duplicated initialization: 01e00ac

💭 Things to be considered

• To remove duplicated codes in gen_img_diffusers.py and sdxl_gen_img.py by using new get_my_scheduler() and line_to_prompt_dict()
  • I tried to do this at the same time, but it seems to require a big change, so I only made this small change (Add --ss in training) for this pull request

[kohya-ss]

Thank you for this. This is really useful!