feat(plugin-js-packages): add default packageManager

[BioPhoton]

User story

As a developer I want to have the minimum setup possible and best smart defaults. In the plugin options the packageManager options is required.

Acceptance criteria

• [ ] in the plugin options the packageManager options is optional
• [ ] in the plugin options the packageManager options defaults to a smart fallback (e.g. derived from the filesystem)

Implementation details

I want to use the plugin like this:

export default {
// ...
plugins: [
  // no options required
  jsPackages()
]
}