[kong] add the ability to include adhoc pod labels

[aspring]

What this PR does / why we need it:

This PR adds the ability to include adhoc pod labels.

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• PR is based off the current tip of the next branch and targets next, not master
• New or modified sections of values.yaml are documented in the README.md
• Title of the PR and commit headers start with chart name (e.g. [kong])

[CLAassistant]

All committers have signed the CLA.

[hbagdi]

I'm not against it but @aspring, can you elaborate on your use-case for this?

[aspring]

We run Kong with Istio and by adding labels to the pod spec they can be utilized by Istio for enhancing tracing as well as visualizations.

[hbagdi]

Interesting. I figured it would always be via annotations but I think label makes sense for this.

[hbagdi]

Please update an existing test file to include a test case.

[aspring]

This should be all set. The following snippet from the test showing the app and environment labels added.

Node:         chart-testing-control-plane/172.17.0.2
Start Time:   Fri, 24 Apr 2020 03:22:06 +0000
Labels:       app=kong
              app.kubernetes.io/component=app
              app.kubernetes.io/instance=kong-5n1v8lzb7n
              app.kubernetes.io/managed-by=Tiller
              app.kubernetes.io/name=kong
              app.kubernetes.io/version=2
              environment=test

[rainest]

This should probably make use of nested items in values.yaml that touch the various places that don't have their own annotation/label sections. Roughly:

metadata:
  deployment:
    labels:
    - foo
    - bar
  pod:
    labels:
    - foo
    - bar
    annotations:
      example.com/example: whatever

However given the existing podAnnotations we'd need to make a breaking change to support it. I don't think that's pressing though, and this is consistent with the existing format, so fine as-is.

[hbagdi]

@aspring Please claim your contributor swag: https://github.com/Kong/kong/blob/master/CONTRIBUTING.md#contributor-t-shirt. Thank you for your contribution.