Provides the ihp-troubleshoot command

This script detects common errors in the dev environment where IHP is running.

The script checks:

• that the current directory looks like an IHP project
• that the .ghci file exists and has the right permissions to be loaded
• that build/ihp-lib symlink exists and references a valid IHP build
• that direnv is loaded correctly into the shell
• that direnv can correctly load the .envrc
• that the digitallyinduced cachix cache is installed
• that the old deprecated cachix key is not used
• nix is correctly installed

Design Goals

The script should be runnable by just downloading a single file. The script should also test that nix is working correctly, so we cannot offer a simple nix package. So this script needs to be a standalone shell script that can be distributed by just downloading the file.