Release 1.39.0

Behavior Changes

• csds: return empty response if xds client is not set (#4505)
• metadata: convert keys to lowercase in FromContext() (#4416)

New Features

• xds: add GetServiceInfo to GRPCServer (#4507)
  • Special Thanks: @amenzhinsky
• xds: add test-only injection of xds config to client and server (#4476)
• server: allow PreparedMsgs to work for server streams (#3480)
  • Special Thanks: @eafzali

Performance Improvements

• transport: remove decodeState from client & server to reduce allocations (#4423)
  • Special Thanks: @JNProtzman

Bug Fixes

• server: return UNIMPLEMENTED on receipt of malformed method name (#4464)
• xds/rds: use 100 as default weighted cluster totalWeight instead of 0 (#4439)
  • Special Thanks: @alpha-baby
• transport: unblock read throttling when controlbuf exits (#4447)
• client: fix status code to return Unavailable for servers shutting down instead of Unknown (#4561)

Documentation

• doc: fix broken benchmark dashboard link in README.md (#4503)
  • Special Thanks: @laststem
• example: improve hello world server with starting msg (#4468)
  • Special Thanks: @dkkb
• client: Clarify that WaitForReady will block for CONNECTING channels (#4477)
  • Special Thanks: @evanj