Future of Localstack

See https://blog.localstack.cloud/the-road-ahead-for-localstack/ :

- the are basically stopping the development of the OSS version
- if we wanna use the docker OSS docker image, we have to pin the version and not use `:latest` (NOTE: we already do that ✔️ )
- the new free version is NOT OSS and requires an auth token (which I think is unacceptable for our developers since I don't want to force people to register with yet another private company)
- the text is a bit vague/unclear if OSS projects (like `object-store`) can get a auth token with CI credits

So while we are OK for now, I think long term we need to figure out what to do. The no-longer-maintained OSS version is probably gonna drift away from AWS S3 over time. I basically see these options:

- **localstack buy-in:** Get a token from localstack for our CI since we're an OSS project. However this is gonna be a bit of a mess for developers that want to debug things, since they now need to play ping-pong with our CI or get their own token.
- **fork:** localstack OSS is Apache-2.0 licensed (need to double check the details!), but we could just fork it
- **another emulator:** We technically only need S3, not the entire AWS stack. Hence we could see if we find another, feature-complete S3 implementation. (e.g. [Garage](https://garagehq.deuxfleurs.fr/), [Moto](https://github.com/getmoto/moto))

Start by reading the linked LocalStack roadmap and reviewing how the pinned LocalStack OSS Docker image is used in CI and developer workflows. Compare the stated options—an OSS-project token, a fork, or another S3 emulator—and define a decided replacement strategy with working CI and local-development support.

Written by the indexing model from the issue text.