add AlertSubscription entity and repository interface
add route for alert_subscriptions
add scope for alert_subscriptions to koauth.php and a2.php
add alert_subscriptions scope to js login logic as well
add AlertSubscription repostiry implementation, also add DI config for this
add migration for alert_subscriptions
add alert subscriptions controller with simple get action
add api-explorer views for alert subscriptions
routing for alert subscriptions: more resource generic config for allowing more actions