Improve FabricIndex handling for Client usages (#674)
* Inject "empty" FabricIndex in Client set
... because if missing the validator might return an error
* Make Tlv encoding writeInteraction aware
In Write interactions the fabricIndex field must be omitted. But we can not omit the whole field because else our schema-aware validation and encoding returns errors. So we add a flag for encoding that do not encode the FabricIndex field.
* Adjust FabricIndex datatype with conditional validation
The FabricIndex datatype accepts when the "OMIT_FABRIC" magic constant is used.
* Add tests
* Changelog
