codeintel: Automatically fetch and index LSIF-referenced NPM dependencies

Created by: varungandhi-src

Builds on top of https://github.com/sourcegraph/sourcegraph/pull/28057 and https://github.com/sourcegraph/sourcegraph/pull/22984/ .

TODOs:

• Add automated tests.
• Figure out where to put the scheme constants. Earlier, I ran into an import cycle error when I did it carelessly. This has some explicit TODOs in the code.

Manual testing steps:

1. Start with sg start enterprise-codeintel.
2. Set npmPackages to enabled under experimental features under site-admin.
3. Refresh and add NPM Dependencies as a code host.
4. Add "[email protected]" under "dependencies" in the code host settings.
5. Turn on auto-indexing and set up a policy. Make sure that repos with URLs matching npm/* will be covered.

6.  npm pack [email protected]
    tar -xzvf got-12.0.0.tgz
    cd package
    git init && git add . && git commit -m "Temp."
    echo '{"compilerOptions":{"allowJs":true}}' > tsconfig.json
    npm install --ignore-scripts
    lsif-tsc -p .
    # Assuming you've got SRC_ACCESS_TOKEN and SRC_ENDPOINT set up in the environment
    src lsif upload -repo=npm/got -root=. -commit=bb23d1f0cb5d634d1da32804860810f8f2d5c176

7. got and its dependencies should be available for search shortly (e.g. try searching for interface).