Add Nix setup with tools for local environment

[mandos]

Should include (versions are not important):

• docker engine (v27.3.0)
• minikube (v1.34.0) with Kubernetes (v1.31.0)
• kubectl (v1.31.2)
• just (1.37.0)
• k9s (0.32.6)
• helmfile (v0.169.0)
• helm (v3.16.3)
• helm plugins:
  • diff (3.9.13)
  • secrets (4.6.0)
• GnuPG (2.4.5)

minikube and docker maybe should be part of host configuration?

Take to consideration that instead of using raw Nix/Nix flakes it can be done with https://devenv.sh/