Add ENTITLEMENT_UPDATE and ENTITLEMENT_DELETE events to webhooks

[thomasgtaylor]

My application has the HTTP interaction endpoint enabled. Currently, only Gateways can receive all entitlement-related events: ENTITLEMENT_CREATE, ENTITLEMENT_UPDATE, and ENTITLEMENT_DELETE.

While workarounds exist for HTTP interaction endpoints, it would be highly beneficial to receive all these events directly (not exclusively CREATE). Without this support, I'm forced to maintain one of the following methods:

1. Making API calls to Discord outside of interaction contexts.
2. Running scheduled jobs to periodically list entitlements and handle expirations.