Hazelnut: de-duplicate Loki alerts

Once we introduce Hazelnut, there are three possible ways to receive alerts from logs:

• Loki
• Hazelnut
• Both

In the third scenario we may be firing alerts twice, which is undesirable.

We should figure out what the plan is to handle this case. Maybe somehow automatically disable one if the other is active, perhaps use Alertmanager inhibition rules to suppress one if the other is fired, or just document "don't do that".