Make sure dns-default pods run on all nodes for 4.18+ clusters

[mmazur]

What type of PR is this?

fix

What this PR does / why we need it?

DaemonSets iptables-alerter (-n openshift-network-operator) and dns-default (-n openshift-dns) should run across all nodes. But for OSD/ROSA Classic they don't due to us having infra nodes and the DSs' tolerations not accounting for that properly (see this thread).

Apparently this has not been an issue in practice thus far, but we probably want this to work as intended going forward, so I've enabled this for 4.18+ clusters only.

Note: this PR only addresses the dns-default pods, since it's not possible to effectively patch the iptables-alerter DS, as that's tightly controlled by its operator and getsquickly reverted.

Which Jira/Github issue(s) this PR fixes?

Fixes OSD-26887

Special notes for your reviewer:

Pre-checks (if applicable):

• Tested latest changes against a cluster

• Included documentation changes with PR

• If this is a new object that is not intended for the FedRAMP environment (if unsure, please reach out to team FedRAMP), please exclude it with:

  matchExpressions:
  - key: api.openshift.com/fedramp
    operator: NotIn
    values: ["true"]

[openshift-ci]

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[mmazur]

/hold

[mmazur]

/unhold

[openshift-ci]

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[bmeng]

I remember @bergmannf was working on the similar thing and turned out it is not working well.
#2144
#2158

[bergmannf]

Thanks for the ping @bmeng - Yes there is an ADR about this, because there are strange edge-cases where we had issues with customer workloads that led to a big escalation.
In case we run this on all nodes it can lead to issues with high-churn clusters - and without the ADR we break the customer being able to decide where to run the pods.

[bergmannf]

/hold