Add Kubernetes CRD Annotations to Duration Type

[ibakshay]

Description

This PR adds Kubernetes CRD kube builder annotations to the Duration type to improve compatibility with Kubernetes Custom Resource Definitions.

Background

The Duration type currently has a custom JSON serialisation that implicitly converts to a string:

Changes

Added annotations to type Duration time.Duration in model/time.go:

// +kubebuilder:validation:Type=string
// +kubebuilder:validation:Format=duration
type Duration time.Duration

These annotations resolve serialization conflicts when Duration is used in Kubernetes CRDs, allowing for correct validation and serialisation in Kubernetes environments while maintaining the existing string serialisation behaviour.

Impact

• Improves compatibility with Kubernetes CRDs
• No change to existing behaviour in non-Kubernetes contexts
• Backwards compatible

Testing

• Verified annotations don't affect existing Duration behavior
• Tested with a Kubernetes operator to ensure proper CRD validation

fixes perses/perses-operator#20