v0.13.7

Changes

Add EastWest Range feature (#1676)
The current east-west communication feature has some problems as the
lack of support for cluster-only routes and the fact that these internal
routes would still be accessible from outside if changing the Host
header. More details of #1526
This commit adds the concept of EastWest Range feature, what makes
possible to define internal domains and custom predicates to Skipper.
With this information, Skipper's Kubernetes dataclient adds the given
predicates on every route identified as part of one internal domain.
Differently from the -enable-kubernetes-east-west and the
-kubernetes-east-west-domain=.ingress.cluster.local flags this feature
will not automatically create routes and both features shouldn't be used
in combination.
It requires changing the current way we convert routegroups to eskip
routes, splitting the hostnames in internal and external hosts. All the
hosts identified as internals require a separated route once it will
have their own ClientIP predicate.
Also, it adds two new flags to skipper configuration,
-kubernetes-east-west-range-domains and
-kubernetes-east-west-range-predicates. It also include the basic
documentation regarding their usage.
This commit creates multiple subsections in the Kubernetes operations
documentation page.

Docker image

Docker image is available in Zalando's Open Source registry:

docker run -it registry.opensource.zalan.do/teapot/skipper:v0.13.7 skipper --help
# arm64
docker run -it registry.opensource.zalan.do/teapot/skipper-arm64:v0.13.7 skipper --help
# arm v7 32bit
docker run -it registry.opensource.zalan.do/teapot/skipper-armv7:v0.13.7 skipper --help