Add health probes to Dozzle container to fix startup race condition

Fixes DEV-350. During pod startup, Dozzle takes ~11 seconds to start
accepting connections, but oauth2-proxy can receive and proxy requests
immediately. This causes "connection refused" errors when users access
the UI right after a pod restart.

Solution:
- Add startupProbe with 30s timeout (15 failures × 2s) to give Dozzle
  time to start without failing readiness
- Add readinessProbe to prevent traffic routing until Dozzle is ready
- Add livenessProbe to restart container if Dozzle becomes unhealthy

All probes use the /healthcheck endpoint on port 8080.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/dozzle/deployment.yaml

@@ -38,6 +38,31 @@ spec:
           value: "X-Forwarded-Preferred-Username"
         - name: DOZZLE_NO_ANALYTICS
           value: "true"
+        startupProbe:
+          httpGet:
+            path: /healthcheck
+            port: 8080
+          initialDelaySeconds: 5
+          periodSeconds: 2
+          timeoutSeconds: 1
+          successThreshold: 1
+          failureThreshold: 15
+        readinessProbe:
+          httpGet:
+            path: /healthcheck
+            port: 8080
+          periodSeconds: 5
+          timeoutSeconds: 1
+          successThreshold: 1
+          failureThreshold: 2
+        livenessProbe:
+          httpGet:
+            path: /healthcheck
+            port: 8080
+          periodSeconds: 10
+          timeoutSeconds: 1
+          successThreshold: 1
+          failureThreshold: 3
         volumeMounts:
         - name: dozzle-data
           mountPath: /data