devshells: Add Delve for debugging (#77)

Add Delve to the devshells; Disable nix hardening for fortify otherwize
delve does not start. See:
https://wiki.nixos.org/wiki/Go#Using_cgo_on_NixOS

nix/devshells/flake-module.nix

@@ -5,6 +5,7 @@
       devShells.default = pkgs.mkShell {
         buildInputs = [
           pkgs.dbmate
+          pkgs.delve
           pkgs.go
           pkgs.golangci-lint
           pkgs.sqlc
@@ -13,6 +14,9 @@
         _GO_VERSION = "${pkgs.go.version}";
         _DBMATE_VERSION = "${pkgs.dbmate.version}";
 
+        # Disable hardening for fortify otherwize it's not possible to use Delve.
+        hardeningDisable = [ "fortify" ];
+
         shellHook = ''
           ${config.pre-commit.installationScript}