Proposal: adjust dockerfiles to use a shared core

> [!NOTE]
> Migrated from [augurlabs/augur#3672](https://github.com/augurlabs/augur/issues/3672)
> Originally opened by `@MoralCode` on 2026-02-10

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Ive seen a pattern used before where parts of a dockerfile can be factored into a shared block.

I wonder if we can use this at a larger scale to:
- deduplicate the two dockerfiles we currently have
- actually commit the patches im carrying for podman (as its own podman-compose.yml)
- allow us to have variations on the config for podman and docker and other backends

fix #130 and #96 and maybe others

Thoughts?

(new contributors please dont make a PR for this until it is discussed)