Support `useCases` from Monocle 7.4

The useCases that are added in Monocle 7.4 are now supported in BackstopJS aswell.
If enabled globally or for a prototype all scenarios for all useCases are defined.

New Settings

Sitegeist:
  Monocle:
    BackstopJS:
      # if enabled only useCases from prototypes that have @styleguide.options.backstop.useCases = true
      # will be included, by default all useCases from the styleguide are included
      useCaseOptIn: false

New @styleguide Annotations

prototype(Vendor.Site:Component) < prototype(Neos.Fusion:Component) {
    @styleguide {
        options {
            backstop {
                # enable or disable the useCases inclusion, the default
                # depends on `useCaseOptIn` settings   
                useCases = true
            }
        }
    }
}