tgswitch: init at 0.5.378

Add tgswitch which allows to easily manage different terragrunt
versions for different projects.

Tested it locally on a NixOS machine:

```
❯ tgswitch --help

Usage: tgswitch [-hv] [-b value] [parameters ...]
-b, --bin=value Custom binary path. For example:
/Users/username/bin/terragrunt
-h, --help displays help message
-v, --version displays the version of tgswitch
Supply the terragrunt version as an argument, or choose from a menu
```

pkgs/applications/networking/cluster/tgswitch/default.nix

···
+{ buildGoPackage, lib, fetchFromGitHub }:
+buildGoPackage rec {
+  pname = "tgswitch";
+  version = "0.5.378";
+
+  src = fetchFromGitHub {
+    owner = "warrensbox";
+    repo = "tgswitch";
+    rev = version;
+    sha256 = "0q2aqh75acbpkmvkws0rl3d5dzq3sisy637c0x6cnc88h34g3n3i";
+  };
+
+  goPackagePath = "github.com/warrensbox/tgswitch";
+
+  meta = with lib; {
+    description = "A command line tool to switch between different versions of terragrunt";
+    homepage = "https://github.com/warrensbox/tgswitch";
+    license = licenses.mit;
+    maintainers = with maintainers; [ psibi ];
+  };
+}

pkgs/top-level/all-packages.nix

···
 
   tfswitch = callPackage ../applications/networking/cluster/tfswitch {};
 
+  tgswitch = callPackage ../applications/networking/cluster/tgswitch {};
+
   tilt = callPackage ../applications/networking/cluster/tilt {};
 
   timeular = callPackage ../applications/office/timeular {};