Add required attribute to generated @JsonProperty on a field

[JaroKuruc]

In order to better support JSON schema generation, it would be helpful if generated @JsonProperty on mandatory fields also contained required=true attribute. This would then be inline with the logic in generated builder which is checking that mandatory fields are set.

[elucash]

thanks for pointing this out! while I'm not aware of much of the functional usage of the JsonProperty.required attribute, but having this attribute set should be good for consistency whether it is functional or just a metadata piece