See if the demo page (index.html) can be automatically updated by the GitHub action

### Description

An example usage appears at https://ytcards.demolab.com/ which is controlled at https://github.com/DenverCoder1/github-readme-youtube-cards/blob/main/api/templates/index.html but it is not updated automatically when new videos are posted or the action is modified.

`readme_path` should allow specifying the path to the index.html and the output type of `html` should allow it to work in an html file.

This could be a separate workflow or added to the existing youtube cards workflow as a second step.