grpc: Allow to set parent context to a client to propagate stream info (#13356)

This patch allows to set parent context which carries the current request stream info to a gRPC async client instance.

Risk Level: Low
Testing: Added
Docs Changes: Updated
Release Notes: Added
Fixes #13345

Signed-off-by: Dhi Aurrahman <dio@tetrate.io>

Mirrored from https://github.com/envoyproxy/envoy @ e5aa69658c6182dd41b6217ec7f6c4c00cac84b4

envoy/config/core/v3/grpc_service.proto

@@ -286,8 +286,10 @@ message GrpcService {
   // request.
   google.protobuf.Duration timeout = 3;
 
-  // Additional metadata to include in streams initiated to the GrpcService.
-  // This can be used for scenarios in which additional ad hoc authorization
-  // headers (e.g. ``x-foo-bar: baz-key``) are to be injected.
+  // Additional metadata to include in streams initiated to the GrpcService. This can be used for
+  // scenarios in which additional ad hoc authorization headers (e.g. ``x-foo-bar: baz-key``) are to
+  // be injected. For more information, including details on header value syntax, see the
+  // documentation on :ref:`custom request headers
+  // <config_http_conn_man_headers_custom_request_headers>`.
   repeated HeaderValue initial_metadata = 5;
 }

envoy/config/core/v4alpha/grpc_service.proto

@@ -292,8 +292,10 @@ message GrpcService {
   // request.
   google.protobuf.Duration timeout = 3;
 
-  // Additional metadata to include in streams initiated to the GrpcService.
-  // This can be used for scenarios in which additional ad hoc authorization
-  // headers (e.g. ``x-foo-bar: baz-key``) are to be injected.
+  // Additional metadata to include in streams initiated to the GrpcService. This can be used for
+  // scenarios in which additional ad hoc authorization headers (e.g. ``x-foo-bar: baz-key``) are to
+  // be injected. For more information, including details on header value syntax, see the
+  // documentation on :ref:`custom request headers
+  // <config_http_conn_man_headers_custom_request_headers>`.
   repeated HeaderValue initial_metadata = 5;
 }