Adapt pipeline examples and scheduler's to huggingface diffusers interface

[mspronesti]

This PR aims at generalizing the three pipeline examples to make them work with the schedulers that need to scale the denoising model input depending on the current timestep and that have a initial noise standard deviation that depends on the timesteps.

This is done making all of them implementing the following methods

• init_noise_sigma
• scale_model_input

The pipeline examples are modified as follows:

• the initial latents are rescaled by the scheduler's init_noise_sigma
• the latents are first passed to the scheduler's scale_model_input method before being fed to the unet forward pass.

[LaurentMazare]

Looks good both for the scheduler itself and for the enhanced api, thanks!