Add VSMSettings struct and equivalent yaml file

[ufechner7]

• add vsm_settings.yaml and vsm_settings_dual.yaml
• add VSMSettings struct
• add SolverSettings struct
• add WingSettings struct
• implement constructor for WingSettings
• implement constructor for SolverSettings
• add tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files with missing lines	Coverage Δ
src/VortexStepMethod.jl	2.63% <ø> (ø)
src/precompile.jl	100.00% <100.00%> (ø)
src/settings.jl	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[1-Bart-1]

Looks good!