[DOCKER] Pandoc: add wordcount custom filter

[marco-lancini]

No description provided.

[github-actions]

Image: 📋 pandoc

	Step	Result
📖	Build	success
🛡	Trivy	success

Build:

Build output

  "containerimage.config.digest": "sha256:089235c43f989a181692c4c3f193be0cb0813c1a32fc718643d3cbd5df050819",
  "containerimage.descriptor": {
    "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
    "digest": "sha256:8b0c53e666066a61e4fd4e4db83edff121de3026c066baa6546693d45545274d",
    "size": 5599,
    "annotations": {
      "org.opencontainers.image.created": "2023-09-21T09:14:30Z"
    },
    "platform": {
      "architecture": "amd64",
      "os": "linux"
    }
  },
  "containerimage.digest": "sha256:8b0c53e666066a61e4fd4e4db83edff121de3026c066baa6546693d45545274d",
  "image.name": "docker.io/library/pandoc:latest"
}

---

Pusher: @marco-lancini, Action: pull_request