feat: Implement paths and ext options for include

[lforst]

Ref: #62

This PR adds the logic to grab files the user configured via include and paths and applies logic for the correct release artifact prefixes:

• If the user points paths to a file, it's artifact path will be its basename prefixed with the urlPrefix (eg. /foo/bar/baz.js -> ~/baz.js)
• If the user points paths to a directory, the plugin will include all the files recursively included in that directory. The file's artifact paths will be the file path, but the part that the user provided via paths is replaced with the urlPrefix.

We also filter based on file extensions with the ext option.

[Lms24]

Looks good to me!
Just a couple of super-l nits and questions but nothing blocking.

Let's not forget to add a note to MIGRATION.md that we're not supporting globs anymore (doesn't have to happen in this PR though)