Emit audit events for workspaces

Add audit events for all things related to workspaces. This would be especially useful before we add billing.

More info (from Slack internal thread)

• we are releasing streaming audit events at an instance level soon: Emit Instance Level Streaming Audit Events (&6125 - closed)
• We also have an Epic where we are tracking adding more audit events Comprehensive audit log (&736) - Individual groups are responsible for adding audit events for their part of the codebase.
• https://docs.gitlab.com/ee/api/events.html
• You can see all the current event types in ee/config/audit_events/types/
• https://docs.gitlab.com/ee/administration/audit_event_streaming.html
• Internal slack channel: #g_govern_compliance