unet_lr is ignored in DAdaptation

[guaneec]

AFAIK, the lr values of the param groups other than the first (0th) group aren't actually used in DAdaptAdam. This makes unet_lr unused in prepare_optimizer_params if the text encoder is also trained.

Maybe a warning should be raised for this? Alternatively, we can either patch DAdaptAdam or manually rescale the params passed to the optimizer.

[kohya-ss]

Thank you for letting me know! The patching seems to be quite difficult, so I've added warning message like this:

when multiple learning rates are specified with dadaptation (e.g. for Text Encoder and U-Net), only the first one will take effect /
 D-Adaptationで複数の学習率を指定した場合（Text EncoderとU-Netなど）、最初の学習率のみが有効になります: lr=1.0