Spike: index npm lockfiles

Created by: olafurpg

To implement the prototype for RFC 593 we need a lockfile indexer for npm and yarn https://docs.google.com/document/d/1SkM8CG0IksvPEKRBRVLKipiRJTopx6Vq_hSWRJ9NyKs/edit#heading=h.trqab8y0kufp

Open questions:

• How to pass named arguments to a predicate? For example repo:dependencies(github.com/sg/sg, kind:npm file:client/web)
• Create npm package repos on demand when we encounter new dependencies. Is it best to insert them into lsif_dependencies table?