KCP: support pluggable in-cluster DNS providers

[ncdc]

User Story

As a user, I would like to create a new cluster using an in-cluster DNS provider of my choosing, instead of having kubeadm install CoreDNS, because I'd like to use something other than CoreDNS from the start.

As a user, I would like to manage my in-cluster DNS provider separately from KCP, decoupling their lifecycles, so that I'm in control of my DNS provider.

(Maybe out of scope?)
As a user, I would like to influence the initial CoreDNS configuration when bootstrapping my control plane, because my cluster needs custom CoreDNS settings to function correctly (both at bootstrapping time and beyond).

(Maybe out of scope?)
As a user, I would like an easy way to manage my CoreDNS configuration, including preserving my customizations when CoreDNS is upgraded.

Detailed Description

See user stories

Anything else you would like to add:

Something like a CoreDNS Operator might be useful or necessary for some of these stories.

kubeadm is currently responsible for installing CoreDNS and we'll need to be able to disable that.

/kind feature
/milestone Next

[neolit123]

similar comment as in:
#3700 (comment)

the current way is by passing --skip-phase=addons or a specific addons/x.
but i guess for CAPI this has to be supported via the config:
kubernetes/kubeadm#2261

[fejta-bot]

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[fabriziopandini]

/lifecycle frozen

[vincepri]

Close in favor of #5491
/close

[k8s-ci-robot]

@vincepri: Closing this issue.

In response to this:

Close in favor of #5491
/close

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