Add ControlNet

[carson-katri]

This adds support for ControlNet.

A ControlNet model can be specified in the "Source Image" panel when using the "Modify" action.

ControlNet models can be downloaded via the add-on preferences, and will show up as a "ControlNet" type.

Note The diffusers cache directory changed, and it did not properly migrate my models. I had to move some folders around manually after updating to main.

[carson-katri]

I think this has a good minimum set of nodes to be useful, especially for more complex tasks like multi-ControlNet. Other nodes for upscaling, more ControlNet annotations, etc. could be added in separate PRs so this doesn't get ridiculously large.

I'll document this in a separate PR as well, along with some example scene files.

[NullSenseStudio]

Ran into quite a few issues though I think most are only caused by platform differences.

[NullSenseStudio]

Download progress appears a little glitchy due to it downloading all files at the same time instead of sequentially, but that could be cleaned up in another PR.

And I missed one fix in the depth render.

Otherwise, LGTM

[bsmith1310]

Wow! Thanks @carson-katri, and @NullSenseStudio!

This is exactly what I was trying to find and I see this was merged just hours ago. I'm going to try to set this up on a fresh environment, can't wait to give this a try!