(WIP) Re-hosting Docs

[kingdonb]

I've built this thing in such a way that the serving image (nginx) doesn't need to change much, because it points to a static image tag, an environment tag that is moving whenever a new tag is tagged.

I've also separated the content into its own OCI image, so that serving can always pull the latest docs tag. There's nothing to kubectl apply unless the Nginx configuration has changed, as there is no new serving image, just a new site content image that gets pulled at runtime, that contains only the HTML and site content for serving.

I'm using this to wrap my brain around Flux's new OCI support, which includes cosign verification. I have keylessly signed the docs image, but I am not verifying the signature (or doing anything with the signature)

The main goal was just to give you a new CI process that builds an image that you can deploy to get the latest docs out, and make it easy to update the docs when you need to push a new version. So after a new tag is pushed, just the HTML gets updated in an image by itself, and as soon as rollout restart is over, the site is automatically upgraded.

The client-side caching isn't quite right, so you still need to Ctrl+Shift+R in order to get the latest version when I tested.

But this is pretty close! And it's very builder pattern, I should be able to make this better and get it ready for the next release 👍