Add support for the special '-' FILE to print to on screen/to stdout in `inventory`

[tdruez]

When running inventory, I want to output the result in stdout instead of creating new file.

See for example scancode-toolkit:

Scan the 'samples' directory for licenses and package manifests. Print scan
  results on screen as pretty-formatted JSON (using the special '-' FILE to print
  to on screen/to stdout):

      scancode --json-pp - --license --package  samples

or python-inspector

python-inspector --help

Use the special '-' file name to print results on screen/stdout.

For example, display the results of resolving the dependencies for
  flask==2.1.2 on screen::

      python-inspector --spec "flask==2.1.2" --json -

Note that this should be added to all commands that require an OUTPUT file argument.