Injections for java.util.Optional<> should be automatic optional

The current approach to support optional injections requires to annotate the field with @Optional plus proper handling within the javacode (null checks etc), which can be forgotten.

So instead of

@Inject @Optional
String fieldname;

it should also be possible to use this

@Inject
Optional<String> fieldname;

with the very same semantic. But the developer is forced to deal with the case that the value is not present.