Fix sub group audit event streaming

What does this MR do and why?

Streaming audit event is top-level group feature to receive all audit events about the group, its subgroups, and projects as structured JSON. Doc link

Currently there several events not follow the strategy:

• any event on sub-group
  • sub group create/update/destroy events
  • sub group deploy token create/destroy/revoke events
• group/project destroy event

fix way

• for sub-group events
  • change audit_event root_group_entity from entity to entity.root_ancestor
• for group/project destroy event
  • add instance variables @entity, @root_group_entity and @root_group_entity_id in audit_event model
  • set @entity after entity destroyed
  • pass json format data with root_group_entity_id to AuditEventStreamingWorker

/cc @daveliu