[Feature]: Extend websocket endpoint for subscription detail pages

[wouterhhuisman]

What should we build?

This ticket builds upon the ticket https://github.com/workfloworchestrator/orchestrator-core/issues/502.

Tasks

• [ ] Make the /api/ws/events endpoint emit the message {"name": "invalidateCache", "value": ["subscriptions", "<subscriptionId>"]} to trigger subscription detail page invalidation.

This event should be emitted from

• The workflow step which also updates the subscription's cached domain model
• The 'set in sync' endpoint
• The update customer subscription description endpoint
• ... ?