Enabling OpenCensus Shim for metrics when using Java agent

[SanjayVas]

If I'm already using the Java agent for automatic instrumentation, how do I enable the OpenCensus Shim for metrics? From the README:

Applications also need to attach OpenCensus metrics to their metric readers on registration.

Of course, with the Java agent we have no need to initialize the OpenTelemetrySdk. My goal is to enable the shim reusing the same configuration as the agent.