Expose step size parameters for AutoFiniteDiff

[1-Bart-1]

When using AutoFiniteDiff, one should be able to change the absstep and relstep parameters as described in the FiniteDiff.jl documentation. This seems to be impossible with the current DifferentiationInterface.jl API.

From this question on the Julia discourse: https://discourse.julialang.org/t/changing-the-relstep-of-autofinitediff-in-an-optimizationfunction/125004

[gdalle]

This will first require SciML/ADTypes.jl#101 to be implemented on the ADTypes side, and then we can take it into account here! Do you want to give it a try?

[1-Bart-1]

Try as in forking ADTypes.jl, adding the changes and creating a pull request there? I can try doing that!

[gdalle]

Yes exactly!

[1-Bart-1]

SciML/ADTypes.jl#102

[gdalle]

@1-Bart-1 wanna try to make the modifications on this side now that the new version of ADTypes has been released?

[1-Bart-1]

#693