Add interval secs

Part of #568

src/routes/settings.js

@@ -158,6 +158,7 @@ function setBackupConfig(req, res, next) {
 
     if (typeof req.body.provider !== 'string') return next(new HttpError(400, 'provider is required'));
     if (typeof req.body.retentionSecs !== 'number') return next(new HttpError(400, 'retentionSecs is required'));
+    if (typeof req.body.intervalSecs !== 'number') return next(new HttpError(400, 'intervalSecs is required'));
     if ('key' in req.body && typeof req.body.key !== 'string') return next(new HttpError(400, 'key must be a string'));
     if ('syncConcurrency' in req.body) {
         if (typeof req.body.syncConcurrency !== 'number') return next(new HttpError(400, 'syncConcurrency must be a positive integer'));