Support out_dim argument for Attention block

Is your feature request related to a problem? Please describe.
When i feed the out_dim argument in __init__ in Attention block it will raise the shape error, because the query_dim != out_dim. In this case, the following code try to keep the given channel of hidden_states.

https://github.com/huggingface/diffusers/blob/b69fd990ad8026f21893499ab396d969b62bb8cc/src/diffusers/models/attention_processor.py#L1393
But it should change the channel as the output of hidden_states = attn.to_out[0](hidden_states).

Describe the solution you'd like.
I suggest the change of code base : https://github.com/huggingface/diffusers/blob/b69fd990ad8026f21893499ab396d969b62bb8cc/src/diffusers/models/attention_processor.py#L1393
to hidden_states = hidden_states.transpose(-1, -2).reshape(batch_size, -1, height, width), then it will respect the channel of hidden_states.
Maybe I will make a PR later.

Describe alternatives you've considered.
None.

Additional context.
None.

src/diffusers/models/attention_processor.py の Attention ブロックと、1393 行目付近で参照されている処理コードから始めます。query_dim != out_dim で shape エラーを再現し、その後、attention の出力が要求されたチャネル次元を保持することと、既存の attention の動作が変わらないことを確認します。