Optional calculation of the steady-state ergodic distribution

[jlperla]

• [ ] Remove the https://github.com/HighDimensionalEconLab/DifferentiableStateSpaceModels.jl/blob/main/src/types.jl#L364 option
• [x] Create a new option calculate_ergodic_distribution defaulting to true
• [x] Only do https://github.com/HighDimensionalEconLab/DifferentiableStateSpaceModels.jl/blob/main/src/generate_perturbation.jl#L265-L292 if toggle set to true
• [ ] remove the regularization of the V in https://github.com/HighDimensionalEconLab/DifferentiableStateSpaceModels.jl/blob/main/src/generate_perturbation.jl#L270 regardless
• [x] Only calculate https://github.com/HighDimensionalEconLab/DifferentiableStateSpaceModels.jl/blob/main/src/generate_perturbation_derivatives.jl#L159-L160 if toggle set to true
• [x] Add in option in the convenience constructor of https://github.com/HighDimensionalEconLab/DifferentiableStateSpaceModels.jl/blob/main/src/sequential.jl#L3-L9 to pass in the u0_prior instead