Add AutoDiffractor

[gdalle]

Is your feature request related to a problem? Please describe.

Diffractor.jl is now a usable AD library in forward mode, but it is not part of ADTypes.jl

Describe the solution you’d like

A new struct called AutoDiffractor.

Describe alternatives you’ve considered

We can also base it on ChainRules.jl with AutoChainRules(DiffractorRuleConfig())

Additional context

@oxinabox what information or parameters would you put in an AutoDiffractor struct? Examples:

• AutoFiniteDiff has the finite difference scheme
• AutoForwardDiff has the number of chunks

[oxinabox]

I don't think we need any struct fields right now.
There is some stuff coming that might need type-parameters, but right now it is basically configuration free.