[DMN Designer] Support Decision Service invocation

User is not able to model a DMN model where he declare a Decision service and invoke this Decision Service from other node, because the Decision Service node doesn't allow any incoming nor outgoing connections.

Acceptance criteria

• Import attached model a1
• Connect mood decision service and Decision-1 decision node
• Deploy the model
• Try to evaluate model via a rest call
• Check the output json doesn't contain error.log
• Check the server log doesn't contain server-error.log