fix: Fix Kubernetes cluster domain parsing from resolv.conf

[sbernauer]

Description

This fixes a bug on AWS EKS:

Given the resolv.conf

search default.svc.cluster.local svc.cluster.local cluster.local ec2.internal
nameserver 172.20.0.10
options ndots:5

the operators logged

retrieve_cluster_domain: stackable_operator::utils::cluster_domain: Using Kubernetes cluster domain from "/etc/resolv.conf" file cluster_domain=ec2.internal.

However, they should have used cluster.local. This PR fixes that.

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

# Author
- [ ] Changes are OpenShift compatible
- [ ] CRD changes approved
- [ ] Integration tests passed (for non trivial changes)

# Reviewer
- [ ] Code contains useful comments
- [ ] (Integration-)Test cases added
- [ ] Documentation added or updated
- [ ] Changelog updated
- [ ] Cargo.toml only contains references to git tags (not specific commits or branches)

# Acceptance
- [ ] Feature Tracker has been updated
- [ ] Proper release label has been added

[NickLarsenNZ]

LGTM

[sbernauer]

Let's merge this, knowing that we will very likely rip out the parsing in the very near future, just to avoid re-adding a buggy version.

[maltesander]

LGTM!