StaticDiscoveryResourceDefinition allows undefined values for its attributes

StaticDiscoveryResourceDefinition reuses the AttributeDefinitions from RemoteDomainControllerAddHandler, but those ADs allow undefined. That's appropriate for that OSH, but not for the StaticDiscoveryResourceDefinition ADs.

Also, the RemoteDomainControllerAddHandler AD's could use some clarification and validation as well, e.g. use setRequires(...) on the builder such that each of protocol, host, port requires the other two. So none are required, but if any is set all 3 must be.

The StaticDiscovery constructor should validate inputs with assert statements and javadoc its parameters, include whether null is allowed. (A null protocol or host will result in an IAE in discover(), so the current code does not support null.)

The DiscoveryOption interface should document whether the 3 "get" methods can return null.