add ghp (GitHub proxy) deployment

Deploy goodtune/ghp so estate agents have a GitHub proxy. Mirrors the
artifactapi app structure under apps/base/ghp with a CNPG Postgres backend,
VSO-synced GitHub App + encryption secrets, an internal Vault-PKI serving cert,
a PreSync migration hook, and platform ApplicationSet/project registration.

argocd/applicationsets/platform.yaml

@@ -26,6 +26,7 @@ spec:
       - path: apps/overlays/*/elastic-system
       - path: apps/overlays/*/encapi
       - path: apps/overlays/*/externaldns
+      - path: apps/overlays/*/ghp
       - path: apps/overlays/*/gitea
       - path: apps/overlays/*/grafana-system
       - path: apps/overlays/*/inteldeviceplugins-system