chore(ci): Create continuous integration and deployment pipelines

[hairmare]

• Run next lint on pull requests
• Publish container images to ghcr.io based on rabe actions.

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[hairmare]

I want to revisit this change before considering this PR ready.

Setting the hostname to ** is most likely a security issue, but we do want to allow several hostnames so we can use the same CI built image without having it be rebuilt for each hostname. The patterm *.rabe.ch might fulfill this, or we add a regex that is more specific.

Potentially we could go even further and also add pathname to narrow down the allowed image URLs.

Note to self: the docs for the feature are here: https://nextjs.org/docs/pages/api-reference/components/image#remotepatterns (and the env vars are defined in next.config.js).

[hairmare]

I changed it to *.rabe.ch during build-time in the CI pipeline, but that pattern still allows sites like share.rabe.ch.

Preferably we would like for it to not be possible to optimize content from ownCloud via nextjs.