Epic: How do clients get adequate metadata providers?

[msarahan]

There's a chicken-egg problem with metadata providers. We don't want installers to have to run metadata providers, because we want resolution to not require dynamic execution of an outside program. Instead, we want to run metadata providers at some point prior to the installer, and then provide the cached static metadata to the installer.

Since there can be arbitrary metadata providers, we need a way of collecting and downloading metadata providers that have what is necessary.