Refactor to define events in the interaction intents

#### Current problems

Currently the non-blocking events are dispatched in nodes, but in some scenario we may want to skip some of the events. e.g. `NodeDoCreateIdentity` will need to skip the create identity event when it is user signup / anonymous user promotion flow. Now we check the graph in the node to determine these cases which add unnecessary dependency to the node.

#### Suggested solutions

Refactor to make the nodes independent to the graph. Each flow should have its own intent, the events should be defined in the intent.

Start by tracing NodeDoCreateIdentity and the interaction flows that dispatch its non-blocking events. Read how nodes currently depend on the graph and how intents are represented. Done means each flow defines its own events in its intent, nodes are independent of the graph, and the signup or anonymous-promotion flow can skip the create identity event.

Written by the indexing model from the issue text.