parser-v2: Extend DeserializationUtils methods to enable providing a custom YAMLMapper

[CalemRoelofsSB]

This PR adds the possibility to set a custom YAML mapper for parsing OAS 2.0 documents with DeserializationUtils methods.

[CalemRoelofsSB]

@frantuma totally agree, have updated it now to accept a YAMLFactory and create the mapper using it from the ObjectMapperFactory in swagger-core