No validation on constructing objects that have required fields

[xibz]

If a field is required, then we should enforce it in the constructor or when calling build (if we have a builder).

sdk-java/sdk/src/main/java/dev/cdevents/models/build/started/Subject.java

Lines 23 to 29 in 5d17b75

	/**
	*
	* (Required)
	*
	*/
	@JsonProperty("id")
	private String id;

But no validation

[aalmiray]

I believe the jsonschema2pojo plugin has a setting for generating a constructor for all required fields. Be mindful that adding such constructor and removing the default one constitutes a breaking change.

cc: @afrittoli @rjalander