Add supervisor-driven ORCA load reporting

[samuel-williams-shopify]

Summary

• sample per-worker CPU utilization and request throughput in the supervisor process
• serve out-of-band ORCA reports alongside ADS
• publish distinct worker identities and configure Envoy client-side weighted round robin
• document the TCP endpoint and Envoy 1.39 requirements

Depends on socketry/async-service-supervisor#10 and socketry/async-grpc-xds#3.

Validation

• bundle exec sus
• bundle exec bake decode:index:coverage lib
• changed library files have 100% test coverage