Add validation handling to Invoke processing (#580)
* Add validation handling to Invoke processing
This PR is adding two things:
* Validation of request data for invoke request
* thrown ValidationError's are converted into a ConstraintError StatusCode like required in specs
* Add FabricIndex injection because missing/implicit in the logic
* Adjust tests
* Make ValidationError a StatusResponseError
* Remove unneeded Error conversion
* Adjust gitignore
* Fix tests
