keep registry accounts for the whole cluster and use them everywhere

- Registry accounts are kept in /etc/pve/priv/proxmenux/registry-auth.json, shared by every node, unless REGISTRY_AUTH_FILE says otherwise
- The custom image importer offers to sign in when a registry refuses an image, and reads it again
- Installers, updates, the watchdog and the Monitor update check read private images with the saved accounts
- The host backup includes the accounts, and uninstalling ProxMenux removes them and keeps the OCI records of the cluster
- Spanish written by hand and spacing fixed for the registry account messages in every locale
- Docs: private registries section, Registry accounts in the OCI menu, README storage notes

web/messages/en/docs/oci-manager/index.json

@@ -41,6 +41,7 @@
               "<strong>Search applications</strong> — search by name across the catalog.",
               "<strong>All applications</strong> — the complete catalog, with the number of applications.",
               "<strong>Manage installed OCI applications</strong> — update, modify, remove or recover what was installed.",
+              "<strong>Registry accounts</strong> — the accounts used to install and update images from private registries.",
               "<strong>Install an image that is not in the catalog</strong> — translate a Compose file, a <code>docker run</code> command or an image reference.",
               "The catalog categories, each with its number of applications."
             ]