Add SPADE normalisation option for diffusion models

[virginiafdez]

Based on the work in: https://arxiv.org/abs/2207.00050
Basically consists on allowing for SPADE normalisation on the upsampling branch of the diffusion model unet.

• Implement SPADE-norm
• Allow for SPADE-norm in diffusion models (requires new input arg to the forward method of the Unet, or the coding of a new Unet allowing for this)
• Allow for SPADE-norm in VAE (in case of latent diffusion models, it might be necessary to condition as well on the VAE side). Same 2 possibilities as in previous point: modify original VAE to allow for input segmentation conditioning, or add new VAE.