[READINESS] Add functionality to check services without Selector

Services can be defined without Selector, but via EndpointSlices
(https://kubernetes.io/docs/concepts/services-networking/service/#services-without-selectors)
This was not covered by the ready.py and is now added.

Issue-ID: OOM-3280

Change-Id: Ie386257bd6533cb735ab872b70a2ecd845ee424a
Signed-off-by: Andreas Geissler <andreas-geissler@telekom.de>
1 file changed