Enable Crons monitors to have tags

Today, it is not possible to add tags to different monitors as a way to group them. This feature can be helpful for creating custom alerts based on a tag or search for all related monitor issues with such tag. Example, let's say I have the following monitors: - send-invoices - send-billing-reminders - process-invoices It'd be good to group them with a tag `billing` and be able to create an alert rule to match any Cron issues with the tag `billing`.