feat: add more_fields

[whywaita]

Hi contributors, Thank you for your great works :)

This change is adding the parameter more_fields.
more_fields can write any data to Slack notify.

example

workflow:

      - uses: lazy-actions/slatify@master
        with:
          job_name: 'test'
          type: ${{ job.status }}
          url: ${{ secrets.SLACK_WEBHOOK_URL }}
          token: ${{ secrets.GITHUB_TOKEN }}
          more_fields: '{"aaa": "bbb", "ccc": "ddd"}'

Slack notify:

note: This slack-notify sent from my sandbox repository. you can check workflow_run in here.

[whywaita]

Hi @homoluctus, Can you review my PR? When I should resolve conflicts from master?

[whywaita]

I resolved conflicts.

[whywaita]

@homoluctus Hi, Can you review this?