Implement automatic unsealing with a secrets controller

Implements an optional integration with the secrets controller to transparently unseal secret characteristics.

As previously discussed in the meeting this was done to allow service designers to design services that use secrets without having to define two versions: one for regular clusters and another for clusters with a secrets controller.

The code uses an enable configuration parameter because its impossible to distinguish between a queue that doesn't have a controller because none was installed or because the controller is down.

Requires org.etsi.osl.model.tmf!37 (merged)

Closes #38 (closed)