The nixpkgs-unstable channel's programs.sqlite was used to identify
packages producing exactly one binary, and these automatically added
to their package definitions wherever possible.
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
```
