Add inactive repos as action output

[akbast]

As defined in #28 The action outputs inactive repos in json format for further actions.

Example usage:

    - name: Run stale_repos tool
      id: stale-repos
      uses: akbast/stale-repos@main
      env:
        GH_TOKEN: ${{ secrets.GH_TOKEN }}
        ORGANIZATION: akbas-orga
        INACTIVE_DAYS: 1

    - name: Print output of stale_repos tool
      run: echo "${{ steps.stale-repos.outputs.inactiveRepos }}"
    - uses: actions/github-script@v6
      with:
        script: |
          const repos = ${{ steps.stale-repos.outputs.inactiveRepos }}
          for (const repo of repos) {
            console.log(repo);
            const issue = await github.rest.issues.create({
              owner: 'akbast',
              repo: 'stale-repos',
              title: 'Stale repo' + repo.url,
              body: 'This repo is stale. Please contact the owner to make it active again.',
            });
            console.log(issue);
          }
        github-token: ${{ secrets.GH_TOKEN }}

Example Issue: akbast#10

[zkoppert]

Thanks for adding this! I've updated the README with your example of usage. Appreciate the contribution!