Consider whether to include public/index.html template as part of @edx/frontend-build

[adamstankiewicz]

This package currently expects the consuming application to have an existing public/index.html template (it will error otherwise).

We may want to explore whether it's possible and/or makes sense to have a default public/index.html template contained within @edx/frontend-build itself so that consuming applications do not need to worry about maintaining their own public/index.html.

However, if an application needs to override a default public/index.html template, it should still be possible to use the public/index.html template from the consuming application.

We should also consider whether this default public/index.html template includes a favicon. For edX microfrontends, the favicon is likely to be the edX logo (eventually pulled from the @edx/brand package), but it likely doesn't make sense to include @edx/brand as a peer dependency of this package, such that @edx/frontend-build remains agnostic.