Don't override index.html

[timhaywood]

Return additional tags rather than a modified html template.

Based on the Vite docs here: https://vitejs.dev/guide/api-plugin.html#transformindexhtml

Also deleted the now unused template file.

fixes #12

[justintaylor-dev]

@timhaywood thanks for getting a start on this!

There are some other items that need to be in place on order for dev and build to work both inside CEP and in the browser.

Branched off and will merge here: #14

[timhaywood]

Thanks so much! Will check out your changes, the CEP world is still mostly a mystery for me :)

Appreciate your fast response!