* chore: refactor CountDashboardsInFolder to use the more efficient Count() sql function
* feat(nested folders): Add CountAlertRulesInFolder to ngalert store
This commit adds CountAlertRulesInFolder and a new model for the CountAlertRulesQuery. It returns a count of alert rules associated with a given orgID and parent folder UID. (the namespace referenced inside alert rules is the parent folder).
I'm not sure where this belongs in the ngalert service, so that will come in a future commit.