[@snowpack/plugin-webpack] Use public path instead of baseUrl

[Kartik Grewal]

Use public path instead of baseUrl in adding resource to html file.

Please refer to this discussion - https://www.pika.dev/npm/snowpack/discuss/498

[Harry Brundage]

I was able to replicate this issue, here's a repository that does so: https://github.com/airhorns/snowpack-webpack-baseurl-example