Add field selector option to Kubernetes strategy

[aj-foster]

Summary of changes

The goal of this PR is to modify the Kubernetes strategy to allow filtering pods by status. This gives users the option to cluster only Running pods and ignore terminating or completed pods. By doing this with a generic field selector option, it provides more flexibility for people to filter by other fields in the future (both for pods and endpoints).

Checklist

• New functions have typespecs, changed functions were updated
• Same for documentation, including moduledocs
• Tests were added or updated to cover changes
• Commits were squashed into a single coherent commit
• Notes added to CHANGELOG file which describe changes at a high-level