introduce nix and flakes

[mahmoudk1000]

Hi,

This PR introduce nix package to devx

This flake.nix defines a reproducible environment for building and using the devx tool, which is used for generating, validating, and sharing configurations powered by CUE. It supports multiple platforms like x86_64-linux, x86_64-darwin, aarch64-linux, and aarch64-darwin.

Key Features:

1. Cross-platform support: Works across different platforms including Linux and macOS.
2. Docker image: It builds a Docker image for easy deployment and containerization.
3. Development shell: It provides a devShell environment with Go development tools (go, gopls, etc.) for local development.

Usage:

To build package: nix build
To build docker image: nix build .#docker
Interactive shell with devx injected in: nix shell
To use the isolated development shell: nix develop

Here view of the power of nix :)