Allow a config option to alter the fail outcome when blocking an issue

[instantiator]

Context

At the moment, when successfully blocking an issue, the action reports a failed state. This seems intentional, and I can understand why you've done it. However, this is the same response we'd expect to see when something went wrong and the action couldn't run to completion (eg. incomplete permissions, couldn't find an issue, etc.)

Desired behaviour

Allow the user to specify an input to determine whether blocking an issue should be considered a successful action, or a failure. (Default behaviour can remain the same.)

eg. something like

    steps:
      - uses: Levi-Lesches/blocking-issues@v2
        with:
          use-label: "blocked"
          fail-on-block: "false"

This means the action can still be used in longer workflows - and will continue to prevent them from completing if the issue is blocked, but users can optionally allow them to run quietly in the background without disruptively showing as errors, by setting fail-on-block: "false"

Workarounds

NB. Setting continue-on-error: true on the step is an OK workaround provided you trust that the action is working. It permits the action to complete without failing the workflow, but cannot distinguish between unintended errors and successfully blocking an issue.

[instantiator]

Added an unsolicited PR - see how you like it!

[Levi-Lesches]

Really hoping people aren't running into random failures! But this can be useful. I'll try to merge that soon