M5: notifications, setup check, audit log and password confirmation

- notifications to administrators for failed backup/restore runs and
  locations without a successful backup for two days (once a day)
- setup check in the admin overview: error when the key/kit is not set
  up, warning for missing, old or failed backups
- security events (recovery kit downloaded, location removed,
  append-only turned off, retention changed, snapshots forgotten) go to
  the audit log and are announced to all administrators, from the web
  and from occ; the scheduled weekly cleanup is logged only
- fix: the recovery-kit download link failed the CSRF check (412); it
  now requires a recent password confirmation instead, like creating the
  key, removing a location and restoring

src/components/RestoreBrowser.vue

@@ -49,6 +49,8 @@ import NcLoadingIcon from '@nextcloud/vue/components/NcLoadingIcon'
 import NcNoteCard from '@nextcloud/vue/components/NcNoteCard'
 import NcSelect from '@nextcloud/vue/components/NcSelect'
 import NcSettingsSection from '@nextcloud/vue/components/NcSettingsSection'
+import { confirmPassword } from '@nextcloud/password-confirmation'
+import '@nextcloud/password-confirmation/style.css'
 import api from '../api.js'
 import { formatSize } from '../format.js'
 
@@ -107,6 +109,7 @@ async function restore() {
 	busy.value = true
 	error.value = message.value = ''
 	try {
+		await confirmPassword()
 		await api.startRestore(target.value.id, snapshot.value.id, selected.value, mode.value)
 		message.value = t('ng_backup', 'Restore queued. It runs with the next cron job; progress is shown under Backups.')
 		emit('changed')