Add Helm Chart to install NKG

[ciarams87]

Proposed changes

Problem:

As a potential user of NKG
I want to use a Helm chart to install the NGINX Kubernetes Gateway
So that I can use one command to install the NGINX Kubernetes Gateway
And so that I can easily update.

Solution:

• Add a Helm chart to install the NGINX Kubernetes Gateway.
• Create a static yaml for njs-module, a make command to generate the file, and add check in pipeline that the njs-modules.yaml file is up-to-date.
• Add make command to lint the helm chart.
• Add deployment instructions.
• Add/ amend developer docs for Helm and for generators
• Add stages in the CI pipeline to lint, test (install only), and publish charts to GitHub charts for edge and tags.

Testing: Local testing - verified local basic installation and modifications to the default values

Closes #614

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[sjberman]

We still need to refine it, but being that this work and #798 are slated for 0.6.0, I wonder if we get the latter done first so that we don't need the njs configmap in our helm chart.

[pleshakov]

Shall we also update the main README?

[ciarams87]

We still need to refine it, but being that this work and #798 are slated for 0.6.0, I wonder if we get the latter done first so that we don't need the njs configmap in our helm chart.

@sjberman I think the work can coexist for now - if #798 gets done first, we can simplify the Helm chart as part of this work. If not, we can do it as part of that one.

[sjberman]

We still need to refine it, but being that this work and #798 are slated for 0.6.0, I wonder if we get the latter done first so that we don't need the njs configmap in our helm chart.

@sjberman I think the work can coexist for now - if #798 gets done first, we can simplify the Helm chart as part of this work. If not, we can do it as part of that one. We'll be removing the nginx-conf ConfigMap too anyway. There's a bit left to do here anyway 😄

The main reason I bring it up is that if we get helm charts released into 0.5, then we break the chart in 0.6 when we change containers up. Not a huge deal since we're still pre-v1, but avoiding breaking changes is nice.

[pleshakov]

could you update the PR description to follow problem/solution template and make sure there is a commit with problem/statement? (according to our guidelines)

[kate-osborn]

🚀