make bootstrap-sass resolving configurable

[vjpr]

Currently bootstrap-sass needs to be resolvable from bootstrap-loader/lib/utils/resolveModule.js.

This means that bootstrap-sass is a peer dependency on bootstrap-loader.

Custom module systems such as pnpm will not be able to find peer deps if they are not explicitly specified in the package.json.

So firstly, it should be declared as a peer dependency. But because you need bootstrap or bootstrap-sass depending on the version, this would create warning messages.

A better approach might be to allow specifying the location of bootstrap-sass or make the resolver context configurable - util/resolveModules.js, resolve.baseDir option.

It's currently not possible to override (pass in as absolute value from ?boostrapPath=) as seen here:

  // Resolve `bootstrap` package
  var bootstrapNPMModule = bootstrapVersion === 3 ? 'bootstrap-sass' : 'bootstrap';

  _logger2.default.debug('Using Bootstrap module:', bootstrapNPMModule);

  config.bootstrapPath = (0, _resolveModule2.default)(bootstrapNPMModule);

...and the config option is not parsed in bootstrap.config.js.

---

FYI: The use case is if you wanted to create a module which contained all bootstrap related stuff to reduce number of deps declared in your app package.json (instead of having to install bootstrap-sass and all the loaders manually).

E.g.

app
  - node_modules
    - webpack-stuff
      - node_modules
        - bootstrap-loader
        - bootstrap-sass
        - style-loader
        - ...

[justin808]

@vjpr Thanks for creating the PR. We should be able to get the merged and shipped soon!