Integrate Nix/Tilt-based workflow from Secret-Operator

[nightkr]

Secret-Operator uses a build workflow based on Nix, crate2nix, and Tilt, which lets us run operators inside of the Kubernetes environment while preserving a relatively tight edit-run feedback loop (compared to our production Docker images which rebuild everything from scratch every time).

I believe this workflow has proven helpful enough in Secret-Op that I would like to propose rolling this out for all operators.

At least initially, this would coexist with (rather than replace) the Dockerfiles that we build production images.

[soenkeliebau]

closed by #212