https://arxiv.org/abs/2204.06125 If it is `None`, no additional embeddings will be prepended.
time_embed_dim (`int, *optional*, defaults to None): The dimension of timestep embeddings.
If None, will be set to `num_attention_heads * attention_head_dim`
embedding_proj_dim (`int`, *optional*, default to None):
The dimension of `proj_embedding`. If None, will be set to `embedding_dim`.
clip_embed_dim (`int`, *optional*, default to None):
The dimension of the output. If None, will be set to `embedding_dim`.