feat: add sd-server API support for steps, sampler and scheduler

[wbruna]

This is on top of #1166 just to make it easier to test.

The step numbers should probably be limited in some way?

[leejet]

I believe it would be better to exclude the Python web client from this PR and keep the scope limited to server-related changes.

[leejet]

The step numbers should probably be limited in some way?

I think we could limit the number of steps to a maximum value, for example, 100.

[Green-Sky]

The step numbers should probably be limited in some way?

I think we could limit the number of steps to a maximum value, for example, 100.

For reference, I have seen distillations that use 150steps as reference.

[wbruna]

For reference, I have seen distillations that use 150steps as reference.

Since this is mostly to avoid excessive processing, a better way could be combining a really high hard limit with a simple heuristic for cost. Something like number of steps * image area * batch size, first capping batch size, then the step count. (out of scope for this PR, of course)