Add a way to provide external-dns with a template to generate service FQDNs

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It'll be great to have the possibility to provide external-dns with a template string like {{.Namespace}}-{{.Name}}.example.com to generate DNS records instead of using the annotation in the service.
Using this template one can manage multiple zones which contains all services without altering the annotation for each service. Also; as far as I understand; currently one service can only map to exactly one FQDN.
Using the templating I can launch one external-dns instance per zone without messing around with my kubernetes service definition.
zalando-mate supports this using --kubernetes-format which was a great fit for our use case.

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Closed. Solved in #160 - confirmed working