Log Message:
grpc: updated to 1.40.0

Release v1.40.0

Core

Update Envoy API to the latest version (2021-07-30).
Enable retries by default.
Add opentelemetry as a submodule for latest xDS API.
Pointing the protobuf submodule to the new URL.
Remove BUILD.gn.
Prevent race causing early-destruction of grpc_winsocket object when creating a \ 
TCP connection.
TLS Security Connector: Add an always-fail-handshaker when certificates are not \ 
ready.
Enable layering checks in the Bazel build.
Support user provided "scope" in JWT and GDC.

C++

C++ opencensus filter: Fix point of creating context for overall call.
Open census call attempt span name and attribute changes
Open census filter: Use new internal stats API and record retry stats.
Add OpenCensus measures and views for retries.

Python

Add retry example for gRPC Python.
Remove Python 2.7 binary wheel generations.
[Aio][fix] catch application exception in request iterators.