Node type property for RuleSet

[makotonakai]

Related to #33 #97

Is your feature request related to a problem? Please describe. Only two end nodes for each connection can detect the end of RuleSet execution, which will trigger connection teardown. However, there is no way for each node to know it is initiator / intermediate / responder.

Describe the solution you'd like Add a property that tells the given node is the initiator / responder / intermediate to RuleSet.

Additional context I think initiator / responder should be eventually integrated to end node, but I will leave it to another issue for the sake of implementation simplicity.