Include advisories and licenses in dependency graphs?

(Originally requested by @agmond in #3.)

Currently, to get a list of the advisories that affect a package version or one of its dependencies, a client:

1. Calls [GetDependencies](https://docs.deps.dev/api/v3alpha/#getdependencies).
2. For each node in the response, calls [GetVersion](https://docs.deps.dev/api/v3alpha/#getversion), ideally making many requests concurrently as in the [package_lock_licenses](https://github.com/google/deps.dev/tree/main/examples/go/package_lock_licenses) example.

If the response from GetDependencies included advisories, only a single call would be needed. The same applies to licenses.

The downside is that the response would be larger (and slower to serve) for all clients, regardless of whether they are interested in advisories (or licenses).