Invalid CLI commands should return non-zero exit code

[FranjoMindek]

Add exitFailure to invalid wasp-cli usages

As far as I can see it works.

➜  waspc git:(bf/franjo/wasp-cli-exit-code) ✗ cabal run wasp-cli asdasdasdasdasd
USAGE
  wasp <command> [command-args]
...

➜  waspc git:(bf/franjo/wasp-cli-exit-code) ✗ echo $?
1
➜  waspc git:(bf/franjo/wasp-cli-exit-code) ✗ cabal run wasp-cli db migrate
USAGE
  wasp db <command> [command-args]
...

➜  waspc git:(bf/franjo/wasp-cli-exit-code) ✗ echo $?
1

Side note:
I think Main.hs is a bit messy currently with the file doing too much work.
There is this note:

-- TODO: maybe extract to a separate module, e.g. DbCli.hs?
dbCli :: [String] -> IO ()

Same should probably be done for AI part.

Fixes #2491

[Martinsos]

LGTM!
Tiny hint: instead of doing

do
  printUsage
  exitFailure

you can do it in one line

printUsage >> exitFailure

You don't have to do, if you find the first one more readable, just wanted to share the tip.

[FranjoMindek]

Thanks for the tip.
Still learning haskell, I'll change it.

[Martinsos]

Thanks for the tip. Still learning haskell, I'll change it.

I know which is why I shared it, but also feel free to keep it as it was originally if you like that better / find it more readable!