Automation Event Handler

On NOS, in a multi-layer context, we'd like to be able to identify what event-handlers are contributed in a Studio project.

For now, an event-handler is identified by an eventId and a chainId which is not enough to detect unicity as of the org.nuxeo.ecm.automation.core.events.EventHandlerRegistry is holding all contributions registered by eventId. See: org.nuxeo.ecm.automation.core.events.EventRegistry#putEventHandler.

Ideally, we would need an eventHandlerId for identifying the atomicity of an event-handler and performing usual operations to a contribution: disable, remove, merge.