NGINX Ingress controller version: v0.34.1

Kubernetes version (use kubectl version): 1.18

Chart version: 1.41.3

What happened:

Generated templates include duplicated yaml keys when giving overrides for labels. These are not accepted by static analysis tools (which are increasinlgy used in user space to detect faulty manifests).

However, these are accepted by helm and kubectl, and probably to allow these unstrict overrides and not have to worry about it. However, this is forcibly allowing invalid yaml to be created and propagated as ok practice, which it is not imo.

Example:

labels:
  dupeKey: bla
  dupeKey: dibla

What you expected to happen:

The chart maintainers do not iterate over override labels provided to skip printing the chart provided defaults, leading to duplicate yaml keys.

How to reproduce it:

in the values set:

  metrics:
    enabled: true
    serviceMonitor:
      enabled: true
      additionalLabels:
        release: thenameofyourprometheusyouwishtosendmetricsto

and deploy the chart

/kind bug