Introduce Github Action to build Darwin packages.

[miry]

Allow to run build scripts for darwin to test changes in PR.

Tests

Run a build: https://github.com/miry/distribution-scripts/actions/runs/7476572158

Download the artifact and checked arch:

$ file embedded/bin/crystal 
embedded/bin/crystal: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64]
embedded/bin/crystal (for architecture x86_64):	Mach-O 64-bit executable x86_64
embedded/bin/crystal (for architecture arm64):	Mach-O 64-bit executable arm64

$ ./embedded/bin/crystal --version
Crystal 1.12.0-dev [0b57b6cc8] (2024-01-09)

LLVM: 15.0.7
Default target: aarch64-apple-darwin

PS: Feel free to modify the code or propose any changes, especially in Github action names.