daemon sets: use standardized tolerations for platform ds

[stbenjam]

Managed OpenShift has an issue with platform daemon sets and infra nodes. The infra nodes are tainted as NoSchedule, to avoid customer workloads on them. However, platform workloads should run there, but two daemon sets (iptables-alerter and dns-default) don't tolerate all taints, unlike most daemon sets, which use:

tolerations:
- operator: Exists

Instead, they use:

tolerations:
- key: "node-role.kubernetes.io/master"
  operator: "Exists"

This prevents these pods from running on infra nodes. However, these DS are also marked PreferredDuringScheduling which can cause the tolerations to be ignored (why do we use this?) triggering frequent KubeDaemonSetMisScheduled alerts, disrupting SREs and CI, and blocking ROSA payload readiness.

PRs to fix this:

• OCPBUGS-45341: iptables-alerter daemonset should run everywhere cluster-network-operator#2581
• OCPBUGS-45338: dns-default daemonset should run everywhere cluster-dns-operator#424

This PR enforces the first style.

/hold
Pending discussion

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[candita]

@stbenjam as a part of the discussion, please see and revise the conventions in https://github.com/openshift/enhancements/blob/921f3ec95e7c32b1fb1b91fc3e3662d4fc92da2e/CONVENTIONS.md#taints-and-tolerations.