chore: Make Celery Queue Depth page less

companion to https://github.com/PostHog/charts/pull/773

We've been paging for this daily for more than 10 days. In all of those cases there hasn't been any action and it resolves itself. This creates alert fatigue, so let's make the alert less sensitive.
We can additionally add a non-paging alert, if this is deemed useful.

charts/posthog/values.yaml

@@ -2528,12 +2528,12 @@ prometheus:
 
             - alert: CeleryQueueDepth
               expr: (max (posthog_celery_queue_depth)) > 1000
-              for: 10m
+              for: 60m
               labels:
                 rotation: common
                 severity: critical
               annotations:
-                summary: Celery job execution delayed for more than 10 minutes.
+                summary: Celery job execution delayed for more than 60 minutes.
                 description: |
                   The Celery jobs queue (stored in Redis) is filling up faster than it is consumed. This impacts our
                   monitoring, as some paging monitors depend on metrics exported by Celery jobs.