Includes a SITE attribute in the node event

When a node event is generated, the payload should include a SITE attribute.
The value could have a different semantic, depending on the effort required to implement it:

• it could be the SITE node reference

• it could be a boolean flag indicating if the node belonging to a SITE or not (in this case the attribute should be renamed from "SITE" to "hasSite")

The purpose of the attribute is to allow the event receivers to understand if a node belongs to a site or not.

Acceptance Criteria

Implement, in community-repo the following:

• When a node event is generated

  • if the node belongs to a site, then the event contains the SITE membership information , using one of the two approaches proposed above

  • if the node doesn't belong to a site, then the event doesn't contain any site membership information

• Implement integration tests which validates the two scenarios in the previous points

• Update documentation