Fixes #977: Adding attribute `sort-schemas`

[Maschga]

Hi, This PR adds the functionality I asked for in #977. I locally tested it in the browser and building the project does not trigger any errors.

Even though the feature has not yet been accepted, I have implemented it. Maybe this will help me convince you to add this attribute to RapiDoc. ;-)

If you have any further questions, please feel free to ask.

Many thanks in advance! Maschga