Feature Request: add required/optional parameter to Adjacency Constraints

[ar0551]

Currently all Adjacency/Exclusion Constraints are always required. Adding a required/optional parameters, as it is already available on the global constraints, would allow more flexibility.
Requested here: https://www.youtube.com/watch?v=dnrK8wpUNmg&lc=UgwPz8HAjrYn41xj82R4AaABAg.9I5UwGV4hWB9_56plBVrwP