feat(document): add support for pathsToSkip in validate and validateSync

[AbdelrahmanHafez]

fixes #10353

This still doesn't add support for pathsToSkip for Model.validate(...)` because the current parameters are:

Model.validate = function validate(obj, pathsToValidate, context, callback) { ... }

We can not add it as a property to any of those parameters, so I'll defer implementing it until #10367 is implemented, then it'll make our lives much easier to extend our API.

[IslandRhythms]

ditto everything Val said

[vkarpov15]

Thanks 👍

[AbdelrahmanHafez]

Happy to help 👍