fix: add label to skip coredns injection at cluster creation and start

[maltelehmann]

What

add new LabelClusterCoreDNSDisabled label to track CoreDNS disabled state, such that CoreDNS injection is skipped at cluster creation and start

Why

fixes #1610

Implications

This fix only works for cluster already created with this fix.

[Copilot]

Pull Request Overview

This PR adds a new cluster label to track CoreDNS disabled state and skip CoreDNS injection during cluster creation and startup operations.

• Introduces LabelClusterCoreDNSDisabled constant to track when CoreDNS is disabled
• Updates cluster configuration transformation to detect --disable coredns arguments and set the label
• Modifies cluster startup logic to check the label instead of parsing K3s arguments

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
pkg/types/types.go	Adds new label constant for tracking CoreDNS disabled state
pkg/config/transform.go	Detects CoreDNS disable flag and sets cluster label during configuration transformation
pkg/client/cluster.go	Updates startup logic to use label-based CoreDNS detection instead of argument parsing

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