This commit adds dockerbuild to flakes.nix:
```
nix build .#headscale-docker
```
This uses the Nix infra to build and _does not_ use Dockerfile.
It currently works on Linux (no macOS)
This commit adds a flake.nix build file, it can be used for three
things:
Build `headscale` from local or straight from git:
nix build
or
nix build github:juanfont/headscale
Run and Build `headscale` from local or straight from git:
nix run
or
nix run github:juanfont/headscale
Set up a development environment including all our tools,
- linters
- protobuf tooling
- compilers
nix develop
