feat: add Docker build and Kubernetes deploy workflow

[dervoeti]

• Added a multi-stage Dockerfile
• Added a GitHub Action to build the Docker image, push / sign it, and deploy it to our Kubernetes cluster
• Replaced @sveltejs/adapter-auto with @sveltejs/adapter-node to configure the application for the Node.js environment

I built the Dockerfile locally, deployed it to Kubernetes and tested it, works fine. It seems like I can't test the GH Action without merging it into main though.

How the action works:
The built image is tagged with the commit hash and then the image of the Deployment is updated to that tag, which causes it to restart.

[netlify]

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[lfrancke]

This breaks the Netlify preview. I think we need to keep the auto adapter.

[dervoeti]

This breaks the Netlify preview. I think we need to keep the auto adapter.

Fixed, it is compatible with both Node and Netlify now.