Add an option to specify retention period for artifacts

[yacaovsnc]

#49
#34

Add an option to specify a shorter retention for each artifact:

      - uses: actions/upload-artifact
        with:
          name: my-artifact
          path: ./my_path
          retention-days: 30

If the new retention-days option is omitted or if the input is 0, the artifact will have a default retention of 90 days unless the value is overridden on the repository settings page (coming later). This yaml input cannot be greater than the value specified on the setting page.

Negative values are not allowed, so the artifact will live for 1 day at least.

[konradpabjan]

Great job! 💪 Just a few questions

[sarink]

How do you do this with the node API? import * as artifact from '@actions/artifact';