Added support for a retry interval to monitors

If a check fails and retries are used you can now specify a specific value for that. So you can check faster if the site goes back up again.

server/database.js

@@ -30,6 +30,7 @@ class Database {
     static patchList = {
         "patch-setting-value-type.sql": true,
         "patch-improve-performance.sql": true,
+        "patch-add-retry-interval-monitor.sql": true
     }
 
     /**