[Playbook] Listen/Trigger when relationships to an entity are added or modified

[romain-filigran]

Use case

Be able to trigger/listen a playbook on the adding or modifying relationships on an entity.
Today, adding a relationship to an entity is not seen as an update event. It is therefore not possible to trigger a playbook if a new relationship is added to an entity.

Proposed Solution

Add a new listener based on the entity relationships