Non-zero exit

[adorton-adobe]

Is your feature request related to a problem? Please describe.

UST should exit with a non-zero status code when critical errors are caught.

Describe the solution you'd like

• Call click.exit() at end of run_sync(). Pass an exit_code variable, which is global to app.py and set to 1 when uncaught AssertionExceptions or generic Exceptions are caught
• Log uncaught Exceptions as critical

Describe alternatives you've considered
n/a

Additional context
n/a