fix(loki): unblock gateway rollout on a single node

Chart default is required podAntiAffinity on hostname plus RollingUpdate 25%/25%, which is maxUnavailable=0 at replicas=1: the new pod stays Unschedulable while the old one lives, and the old one never leaves while the new one is not Ready. Null the affinity (an empty map deep-merges with the default and keeps the rule) and set maxSurge/maxUnavailable to 1.

loki/k8s/loki-values.yaml

@@ -73,6 +73,19 @@ backend:
 
 gateway:
   replicas: 1
+  # Single node: chart default is required podAntiAffinity on hostname +
+  # RollingUpdate 25%/25% (effective maxUnavailable=0 at replicas=1).
+  # That deadlocks the rollout: the new pod stays Unschedulable while the
+  # old one lives, and the old one never leaves while the new one is not
+  # Ready. Null clears the default (an empty map would deep-merge with it
+  # and keep the required rule); maxUnavailable=1 allows a brief gateway
+  # outage during rollouts instead of a stuck deploy.
+  affinity: null
+  deploymentStrategy:
+    type: RollingUpdate
+    rollingUpdate:
+      maxSurge: 1
+      maxUnavailable: 1
   resources:
     requests:
       memory: "32Mi"