Signed-off-by: 杨阳 10014842 <yangyang1@zte.com.cn>

The k8s external-dns project now uses the official Kubernetes projects
container registry at k8s.gcr.io. Update all references to use the new
registry.

* Update apiVersions in docs

Update docs to reflect new apiVersions for ingresses and deployments.

* Add selector to apps/v1 deployments

Co-authored-by: Alfred Krohmer <alfred.krohmer@logmein.com>
Co-authored-by: Jonas-Taha El Sesiy <github@elsesiy.com>

Making sure the records are created depends on different settings. Add the section about debugging.

The extensions/v1beta1 API is deprecated for Deployment and with 1.16 is
not served by default anymore. This breaks the examples on k8s 1.16.

See this blog post for details on the deprecations:

https://kubernetes.io/blog/2019/07/18/api-deprecations-in-1-16/

The --istio-ingress-gateway flag may now be specified multiple times.

* add Istio Gateway Source

* add documentation for Istio Gateway Source

* make both istio namespace and ingress gateway service configurable

* prefix gateway types, constructors, and flags with 'istio-'

* fix: add missing sources to source flag docs