feat(tracker): enable tracking of all kustomizations in a cluster

[dblinkhorn]

This PR enables flux-commit-tracker to watch all Kustomization resources in a given cluster, instead of only the Kustomization in its own namespace, as it currently does.

We are keeping the existing metrics model the same: one duration metric per Kustomization apply, using deployment_tools commit timestamps from exporter-info and reconciliation success time from the Kustomization status.

Changes

• Removed the old single Kustomization cache restriction
• Added an in-memory exporter-info cache keyed by repositoryURL/appliedRevision to avoid repeated OCI fetches for the same revision

The tracker now:

• watches Kustomization objects cluster-wide
• ignores unsupported Kustomization objects (e.g. non-OCI Kustomizations)
• records one metric per relevant apply event

NOTE: This PR does not include the deployment RBAC changes that will be needed for the tracker to access all Kustomizations in a cluster. A follow-up PR will address this.

Closes #261.

[juliajohannesen]

Looks good! Thanks for knocking this out!