Add a "create-and-delete-only" policy

[yaronya]

What would you like to be added:
I'd like to have an additional policy called create-and-delete-only, along with the existing ones of sync, create-only and upsert-only

Why is this needed:
I'm using external-dns to create and manage DNS records in Route53. I have a script that initiates a DR process that changes the weights of the DNS records, and I don't want external-dns to update the weights back to their original setting.
I still want it to delete the records in case the ingress is removed, hence the create-and-delete-only

I'm willing to contribute if I get the green light 😃