npmrc registry cafile config not respected

When using a custom registry a custom certificate might also be required. Yarn and NPM support a `cafile` property in the npmrc to specify a custom certificate.

Start by tracing how rules_js reads npmrc settings for custom registries and compare the existing behavior with Yarn and NPM's cafile support. Verify completion by confirming that a custom certificate is honored when accessing a custom registry.

Written by the indexing model from the issue text.