[FEATURE]: come up with a better way to prevent deleting the default endpoint of a service when a GTP is deleted

[shriramsharma]

Is your feature request related to a problem? Please describe. This bug fix https://github.com/istio-ecosystem/admiral/pull/235 was added as a stop-gap approach to a bug that would inadvertently delete the only endpoint for a service in case a GTP is deleted.

The stop-gap approach currently fixes this problem by modifying the event type to Update but this would lead to many orphan endpoints where the intent of deleting a GTP is to remove an endpoint.

Describe the solution you'd like Somehow need to come up with a way to prevent deleting the default endpoint in case a GTP is deleted.