Help message not displayed when `?` is specified for `InteractiveOption` if type is boolean flag

[sphuber]

Example is verdi code setup, when asked whether it is --on-computer (i.e. a boolean flag), when submitting ? instead of a help message, an error with invalid input is returned:

(aiida_dev) sph@citadel:~/code/aiida/env/dev/aiida-core$ verdi code setup
Report: enter ? for help.
Report: enter ! to ignore the default and set no value.
Installed on target computer? [Y/n]: ?
Error: invalid input
Installed on target computer? [Y/n]:

The reason is that click.core.Option.prompt_for_value treats boolean options different from others. Instead of calling prompt if calls confirm. The former respects the value_proc callable to we provide, which allows us to process the value and display the help message if a special character is provided, but the latter only accepts y or n, and so passing ? triggers the error.