move helm charts page to ghpages branch and publish on release

[bwagner5]

1. Issue, if available:
https://github.com/awslabs/karpenter/runs/3965960509

2. Description of changes:
For some reason the pages build and deployment stopped working. We were publishing the whole repo, but since we're hosting https://karpenter.sh w/ Netlify now, we can just publish the charts dir without the docs and website content. Unfortunately, GH pages doesn't allow you to configure a custom directory to deploy in the same branch (only /(root) and /docs). So this PR adds a gh-action that publishes the charts dir to the gh-pages branch which will hopefully avoid running into weird build failures unrelated to the content that we actually care about publishing.

This PR also uses https://charts.karpenter.sh which is currently a CDN distro for the github pages origin/path. But this can be changed in the future if we'd like to move away from GH Pages for helm chart distribution without requiring users to update their helm repo URL.

3. Does this change impact docs?

• Yes, PR includes docs updates
• Yes, issue opened: link to issue
• No

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

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[prateekgogia]

Have you looked at this action from helm helm/chart-releaser-action?

[bwagner5]

I think that action does a little more than we want. In the docs it says it cuts a Github release when it finds a new chart. Maybe that can be disabled, not sure? This might be something to look into though since it would replace the other manual steps we do to create the index. For now, this PR will fix our current process and we can investigate better tooling like this helm gh action when we fully automate the release process.

[ellistarn]

Nice! Approved just in case Prateek's recommendation doesn't pan out.