Add skip-comment flag and input as well as coverage_report output

[jshufro]

Closes #34

An example of it working can be seen here Rocket-Rescue-Node/rescue-proxy#66 (comment)

[fgrosse]

Thanks for the contribution 🙏

I left a couple of comments and will address them myself so we can merge this one quickly. I will test this a bit with one of my repos but plan to wait for your final OK as well so we know it works as expected on your end.

[fgrosse]

I just completed testing the feature via fgrosse/prioqueue#5 where I tried to emulate your use case of adding a prefix to the generated comment. This gives me the confidence to go ahead and merge the PR as it is right now.

In order to use this version in your workflow, you need to make sure, your Leave a comment with a link step treats the newlines from the output string correctly (i.e. keeps them in the string and does not interpolate them inside the javascript code itself). The following approach worked well in my tests:

      - name: Leave a comment with a link
        uses: actions/github-script@v6
        with:
          script: |
            const report = `${{ steps.report-step.outputs.coverage_report }}`;
            github.rest.issues.createComment({
              issue_number: context.issue.number,
              owner: context.repo.owner,
              repo: context.repo.repo,
              body: `[Coverage Report](${{ needs.unit_tests.outputs.html-coverage-url }})\n${report}`
            })