add annotations for fixing 502 status code (#527)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Enhanced ingress settings for Kubeapps deployment, allowing for
increased timeout and body size limits.
- Added configuration options for handling larger requests and longer
processing times.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/system/dashboard/values.yaml

@@ -1,4 +1,11 @@
 kubeapps:
+  ingress:
+    annotations:
+      nginx.ingress.kubernetes.io/proxy-read-timeout: "600"
+      nginx.ingress.kubernetes.io/client-max-body-size: 1m
+      nginx.ingress.kubernetes.io/proxy-body-size: 100m
+      nginx.ingress.kubernetes.io/proxy-buffer-size: 16k
+      nginx.ingress.kubernetes.io/proxy-buffers-number: "4"
   fullnameOverride: dashboard
   postgresql:
     enabled: false