Add capa-capg featureset for gcp-credential-manager

[tamalsaha]

Summary

• add new capa-capg FeatureSet for CAPG clusters
• add gcp-credential-manager feature under capa-capg
• update capi-capa and credential-manager templates for provider-specific behavior and OpenShift distro value handling
• update service-backend ServiceMonitor templating to reuse a single rendered metrics token secret name
• regenerate opscenter-features README/value wiring and refresh catalog artifacts via update-catalog script

Catalog Update Details

• gcp-credential-manager image/tag updated to v2026.3.11
• catalog image list ordering refreshed by generator (including featureset editor entries)

Changed Files

• catalog/feature-charts.yaml
• catalog/export-images.sh
• catalog/import-images.sh
• catalog/copy-images.sh
• catalog/import-into-k3s.sh
• charts/opscenter-features/values.yaml
• charts/opscenter-features/README.md
• charts/opscenter-features/templates/featuresets/capa-capg/featureset.yaml (new)
• charts/opscenter-features/templates/featuresets/capa-capg/gcp-credential-manager.yaml (new)
• charts/opscenter-features/templates/featuresets/capi-capa/aws-credential-manager.yaml
• charts/opscenter-features/templates/featuresets/capi-capa/featureset.yaml
• charts/service-backend/templates/servicemonitor.yaml

Validation

• branch diff vs master: 12 files changed, 83 insertions, 12 deletions
• commits include Signed-off-by footer