Provide kiwi validation constraints via service loader mechanism

[sleberknight]

For background see discussion #689 and Adding custom constraint definitions via the Java service loader.

This change has no impact to existing code other than to ensure kiwi provides its custom validation constraints in a way that they augment custom constraints in an application. Currently, kiwi's custom constraints uses ValidationMessages.properties as its validation messages. The problem is that if an application also uses its own ValidationMessages.properties (which is generally how you implement custom constraints in a service, such as a Dropwizard application) then the application's message bundle overrides the one in kiwi unless additonal steps are taken, for example using the Maven Shade Plugin and an AppendingTransformer to combine all ValidationMessages.properties. And this assumes there are no conflicts in property names in the bundle.

This refactoring uses the method discussed in this blog to use Java's service loader mechanism. It renames the ValidationMessages.properties to ContributorValidationMessages.properties, adds a META-INF/services/jakarta.validation.ConstraintValidator file that contains the list of kiwi ConstraintValidator implementations, and removes the validatedBy from all the validation annotations (which avoids them being found twice, once via the service loader mechanism, and once via validatedBy).

Note that if there are other libraries in an application which also provide their own custom constraints and use the same ContributorValidationMessages.properties, then an additional step is still required to combine these files, e.g., using the AppendingTransformer mentioned above.