Use virtual filesystem to read local Maven settings

[cuixq]

Maven authentication information is stored in local settings.xml.

Considering the extractor uses virtual filesystem, we need to refactor MavenRegistryAPIClient to use the virtual filesystem to read the local settings.

[oliverchang]

I discussed this with @michaelkedar earlier -- this is probably lower priority for now because auth only makes sense in the local developer use case where they have creds on their machine, and having a virtual filesystem isn't as necessary there.