Since you want to embed the chart on an external page, the documentation you found is not the right direction -- that's for creating new plugins or apps within Kibana, not external. Sorry about the confusion.
You can just navigate to the visualization you want to embed, add the filters, then click the Share button to get a URL to use for iframe code in your external page.
- Create the visualization, apply the filters, then save the visualization
- Click "Share" at the top
- Copy the iframe code
- Paste the iframe code into your external HTML
Example, shown on: https://www.w3schools.com/html/tryit.asp?filename=tryhtml_basic
