Add onNixBoot option to dotreplit file

Describe your feature request
The .replit file has an option called onBoot that runs a command when the Repl boots. But when it runs, Nix commands aren’t available. It would be extremely useful if we could get an option called onNixBoot that runs when the Repl boots and Nix packages have been installed.

What problem(s) would this feature solve?
Using Nix commands when the Repl boots.

Explain what you were trying to do when you came across the problem leading to this feature request
Making a shell script that would run on boot, and it needed Nix packages to be installed.


Is nix-shell or nix-env available while booting? If so, can you install packages that you need?