Summary:
Reads `go.sum` to check all golang deps. Tries to fetch license from `github.com` and if it fails, tries `pkg.go.dev`.
Reads `.gitmodules` for submodules and tries to fetch licenses from `github.com`.
Uses the npm `license-checker` package to fetch licenses for npm deps.
Reads `repositories.bzl` for other deps and tries to fetch licenses from `github.com`.

Falls back to reading a manual JSON input for deps that we couldn't automatically fetch licenses for.

Test Plan: Run the license fetcher script.

Reviewers: zasgar, philkuz, #engineering, michelle

Reviewed By: philkuz, #engineering, michelle

Subscribers: michelle

Differential Revision: https://phab.corp.pixielabs.ai/D6652

GitOrigin-RevId: a7afed22cc3d65c4a87fd161f0fb1ce5ef619e60