chore: update default value of dnsPolicy in values.yaml to Default

[jonathan-innis]

Fixes #2186

Description

Updates the default dnsPolicy for the karpenter-controller pod spec to be Default as opposed to ClusterFirst

How was this change tested?

• make test
• Manual deployment validation with make apply

Does this change impact docs?

• Yes, PR includes docs updates
• Yes, issue opened: #
• No

Release Note

None

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

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[ellistarn]

Nice work!

[snorlaX-sleeps]

Just a note incase this causes an issue for other users:
When using a network stack in Kubernetes e.g Istio, Karpenter will fail to start as dnsPolicy: default is connecting to the VPC based DNS servers which don't have any kubernetes services listed.
The istio-proxy needs to connect to the istiod.istio-system.svc which is a kubernetes service and unavailable with the current setting.
The fix is to revert to dnsPolicy: ClusterFirst in the Helm values file

[johngmyers]

Another situation this breaks: running Karpenter on an ipv6-only cluster on a dual-stack node. Using the node's DNS servers, without DNS64, causes Karpenter to attempt connecting to STS using IPv4. Reverting to ClusterFirst causes it to use coredns, with DNS64, so the connections to STS go through NAT64.