expose polynomial:power and cosine_with_restarts:num_cycles params

[zetyquickly]

to get_scheduler func,

• add it to the train_dreambooth.py

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[zetyquickly]

@pcuenca PR to an issue https://github.com/huggingface/diffusers/issues/1232

What's done:

• exposed only two parameters power and num_cycles on top of existing get_scheduler func API. it's possible to expose all of the parameters but taking into account that the issue wasn't there before we've noticed it, I assume it would pile up the code
• changed parameter num_cycles name of the cosine scheduler to not overlap with cosine_with_restarts, because they have different meanings
• added new parameters to the dreambooth's args

Haven't found any test script in test folder that tests optimizers.py