Expand "Optimizersv4" Documentation

Possible classes to highlight:
- [`GradientDescentOptimizerv4`](https://github.com/InsightSoftwareConsortium/ITK/blob/master/Modules/Numerics/Optimizersv4/include/itkGradientDescentOptimizerv4.h)
- [`LBFGSBOptimizerv4`](https://github.com/InsightSoftwareConsortium/ITK/blob/master/Modules/Numerics/Optimizersv4/include/itkLBFGSBOptimizerv4.h)
- [`RegistrationParameterScalesFromPhysicalShift`](https://github.com/InsightSoftwareConsortium/ITK/blob/master/Modules/Numerics/Optimizersv4/include/itkRegistrationParameterScalesFromPhysicalShift.h)
- [`RegistrationParameterScalesFromIndexShift`](https://github.com/InsightSoftwareConsortium/ITK/blob/master/Modules/Numerics/Optimizersv4/include/itkRegistrationParameterScalesFromIndexShift.h)

Could be demonstrated independently as with [Amoeba Optimizer](https://examples.itk.org/src/numerics/optimizers/amoebaoptimizer/documentation) or in the context of registration as in [PlotExhaustiveOptimizer](https://examples.itk.org/src/numerics/optimizers/exhaustiveoptimizer/plotexhaustiveoptimizer).

Start with the linked Optimizersv4 headers and the Amoeba Optimizer and PlotExhaustiveOptimizer example documentation. Determine how the four listed classes should be demonstrated independently or within registration examples. Done means the Optimizersv4 documentation includes useful examples covering the proposed classes.

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