sourcev1: align CRD validation with v1beta2

[kthurman59]

Summary

Align source.toolkit.fluxcd.io/v1 CRD validation with the existing v1beta2 behavior and documentation.

Changes

HelmRepository

• Add a default for .spec.timeout ("60s") so the CRD reflects the effective default.
• Keep .spec.interval and .spec.timeout as string durations with regex validation, matching the existing schema.

GitRepository

• Add Enum and default for .spec.provider (generic, azure, github) so the CRD matches the actual provider options and default.

HelmChart

• Add XValidation so .spec.verify is only allowed when .spec.sourceRef.kind is "HelmRepository", consistent with v1beta2 semantics.

No controller logic changes, only schema-level validation so invalid specs fail at admission instead of at reconciliation.

Testing

On an Ubuntu VM:

• make manifests
• cd api && go test ./...
• export KUBEBUILDER_ASSETS=/home/kevin/src/github.com/kthurman59/source-controller/build/testbin/k8s/1.34.1-linux-amd64
• go test ./...