Give permission responses a lossless replacement for the deprecated namespace and name fields

[AmanGIT07]

internal/reconcile/permission_reconciler.go, cmd/permission.go, and assertions in test/e2e/regression/service_registration_test.go read the deprecated namespace/name response fields because the replacement key round-trips lossily: a namespace without a slash gains a /default suffix through SplitNamespaceResource, and names containing dots fail to split in PermissionNamespaceAndNameFromKey. Fix the key scheme (or add a faithful field), then migrate these readers.

Part of #1782.