Wait until notification types are loaded

[edmundoa]

In order to easily reproduce the issue, I manually added a Thread.sleep(1000) in org.graylog2.rest.resources.alarmcallbacks.AlarmCallbacksResource#available.

Fixes #3534

This needs to be merged into the 2.2 branch as well.

[dennisoelkers]

While this might work, the problem is not solved in the place where it occurs. The race condition occurs in the AlertNotification component, so it should also be solved there, because otherwise it will happen again when that component is rendered from a different component. There are (at least) two ways to solve it there:

a) pass the alert notification type to the AlertNotification component as a prop, or
b) use the store in that component and wait for it to load, rendering a spinner in the mean time.

[edmundoa]

I moved the check to the component itself. The reason to put it in ConditionAlertNotifications before was because that component is the one requesting the data, and it feels more natural to me to group those two actions that are closely related.