[Community] Accept latents as optional input in other pipelines

[pcuenca]

The Stable Diffusion pipeline accepts latents as an optional input for reproducibility purposes, see #247.

In conversation with @tmabraham, he suggested extending this feature to other pipelines too. In addition to reproducibility efforts, this could come in handy for a potential integration with the fastai library.

[patrickvonplaten]

Yes - I think we could/should definitely add this!

[tmabraham]

If you want, you can assign me this, I think I'll work on adding this during this week...

[patrickvonplaten]

This would be very nice @tmabraham !

[daspartho]

Hi, @tmabraham.
If you're not currently working on this, I would be happy to take on it :)

[daspartho]

The Latent Diffusion pipeline presently does not accept latents as an optional input; I'll open up a PR to add it.