chore: add our substituter config to flake.nix (#1839)

Author: jfroche

flake.nix

@@ -1,6 +1,11 @@
 {
  description = "Prototype tooling for deploying PostgreSQL";
-
+ nixConfig = {
+ extra-substituters = [ "https://nix-postgres-artifacts.s3.amazonaws.com" ];
+ extra-trusted-public-keys = [
+ "nix-postgres-artifacts:dGZlQOvKcNEjvT7QEAJbcV6b6uk7VF/hWMjhYleiaLI="
+ ];
+ };
  inputs = {
  nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
  flake-utils.url = "github:numtide/flake-utils";