JsonObject is not by default deserialized by RESTEasy

[xstefank]

Following exception is returned by /pull-request endpoint:

com.fasterxml.jackson.databind.JsonMappingException: Cannot find a deserializer for non-concrete Map type [map type; class javax.json.JsonObject, [simple type, class java.lang.String] -> [simple type, class javax.json.JsonValue]]
 at [Source: (io.undertow.servlet.spec.ServletInputStreamImpl); line: 1, column: 1]

introduced in 28336cf