✨Add event constants for certificate-related automatic actions

[VijetaPriya47]

This commit adds event constant definitions that will be used to emit events for automatic certificate-related actions in KubeadmControlPlane:

• EventKubeconfigCertificateRotated: Emitted when kubeconfig certificate is automatically rotated due to approaching expiry
• EventKubeconfigCertificateRotationFailed: Emitted when kubeconfig certificate rotation fails
• EventCertificateExpiryTriggeredRollout: Emitted when a machine is marked for rollout due to certificate expiry approaching the threshold

These constants provide a foundation for improved observability and monitoring of automatic certificate management operations.
In reference with #13242
and Issue #12930

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Hi @VijetaPriya47. Thanks for your PR.

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[VijetaPriya47]

@sivchari could you review this.