Multiple Callback Subscriptions

We released a change that enables consumers to subscribe to callback events with more than one url.

1. Add Multiple Callback Subscriptions: POST /subscriptions/bulk-upsert

This creates multiple callback subscriptions in a single request; returns both newly created subscriptions and already-existing matches (same eventType + callbackUrl).

Multiple subscriptions per eventType are supported as long as callbackUrls differ.

If a subscription with the same eventType + callbackUrl already exists, it is not modified and is still included in the response.

Only the subscriptions included in the request are affected; other existing subscriptions remain unchanged.

Limit: max 42 subscriptions per event type.

2. Delete Callback Subscription: DELETE /subscriptions/id

This deletes a callback subscription by its UUID. It respond with 204 No Content on successful deletion.