Add option to write output to file

[AdamVB]

Is your feature request related to a problem? Please describe.
If you want to use the junit report feature in github actions, you need to save an artifact file in junit format. This currently isn't possible with the action here as far as I can tell.

Describe the solution you'd like
Add an option to the action like output-to-file: true and output-file-name: report.xml

Describe alternatives you've considered
The alternative would be to call cnspec directly, and then > to file, but this would be more elegant.

Additional context
As shown in the docs here:
https://mondoo.com/docs/platform/infra/supply/cicd/gitlab/#junit-report