Add Dockerfile and container CI

[the-snesler]

This updates the build CI task to create a Docker container and push it to GitHub Container Registry. In the future, we could then pull it down on a server, set the appropriate .env variables, and deploy. Because it uses GHCR's caching, it may be able to speed up build times too.

Most of the code is reused from a combination of https://github.com/the-snesler/buckys-buzzer-beater and https://github.com/docker/metadata-action. This PR already pushed a container that in theory you could download and run right now https://github.com/DSSD-Madison/ST-Madison-Backend/pkgs/container/st-madison-backend

[the-snesler]

Attempted to deploy and getting this error:

called `Result::unwrap()` on an `Err` value: DuckDBFailure(Error { code: Unknown, extended_code: 1 }, Some("IO Error: Extension \"/root/.duckdb/extensions/v1.4.3/linux_amd64_musl/httpfs.duckdb_extension\" could not be loaded: Dynamic loading not supported"))

Back to the drawing board

[the-snesler]

It is working. I switched to prebuilt binaries, and now it is deployed at: http://192.210.203.38:2160/health
I'll give it a domain some other time, but at least it works end-to-end. Does mean I needed to change the README instructions- I am sure we could figure out which folder it looks for DuckDB in, but for now it's easier to just tell it to download every time.

[adrian-brady]

LGTM