Use option key as meta in Alacritty under macOS

To use option key under macOS as Meta key use the option option_as_alt and set it to "Both".

This is the example for the newer Toml file format.

# ~/.alacritty.toml
[window]
option_as_alt = "Both"

And this is the older YAML format.

# ~/.alacritty.yml
window:
  option_as_alt: Both

Check more at https://alacritty.org/config-alacritty.html#s20.