Fix/k8s skip hostaliases for empty services

What does this MR do?

Do not add to k8s executor the services host aliases when no service defined

Why was this MR needed?

Skip adding an empty hostaliases to the executor pod definition for kubernetes when no services are defined.

What's the best way to test this MR?

Start a job on a kubernetes executor without services defined.

What are the relevant issue numbers?

Fix #27248 (closed)