feat(ci): build and publish staging docker images

[hacdias]

Closes #78.

[hacdias]

@aschmahmann do you know why we use our own script to generate the Docker labels instead of something simpler (e.g. https://github.com/docker/metadata-action)?

[lidel]

The way we generate labels comes from go-ipfs and predates Github Actions.

We could refactor it, as long a new method gives us the same level of flexibility around label filenames, but I'd say it is better to use the same setup everywhere (kubo/rainbow/someguy) right now, and spend time elsewhere. Refactor across all repos (in unified fashion) can be done after more pressing IPDX work lands this year.

[lidel]

Lgtm, ported some user-friendly Docker docs.

[lidel]

@ns4plabs @aschmahmann fyi I've created staging branch, and confirmed images for that branch are build correctly:

https://github.com/ipfs/rainbow/actions/runs/7865229424 produced ghcr.io/ipfs/rainbow:staging-2024-02-11-018e2c2, all tags can be listed at https://github.com/ipfs/rainbow/pkgs/container/rainbow/

You can use this setup for deterministic builds that we then can run as staging experiments.