k8s: give nextcloud-local valkey a unique release name
The nextcloud-local valkey HelmRelease reused releaseName 'valkey', which
collides with the shared default-ns valkey release in Flux's flux-system
Helm storage (both write sh.helm.release.v1.valkey.v*). Give it a unique
release name so the two stop overwriting each other's release secret and
flapping on reconcile. Chart resources stay named 'valkey' (Chart.Name),
so valkey.nextcloud.svc is unaffected.