staging/web-cass: Increase resources for the instance

It's currently taking some time to answer and the 2 replicas are roughly at 100% use of
cpu. Let it scale a bit more so it responds better to avoid flip-flop in alerts.

swh/values/staging/swh-cassandra.yaml

@@ -560,7 +560,7 @@ web:
       autoScaling:
         minReplicaCount: 2
         maxReplicaCount: 4  # 4 to test the autoscaling in extreme scenarios
-        cpuPercentageUsage: 1000
+        cpuPercentageUsage: 75
       hosts:
         - webapp.staging.swh.network
         - webapp-cassandra.internal.staging.swh.network