http1: support configuring upstream http/1.1 header casing (#8751)

Wires up the upstream side of HTTP/1.1 header formatting and documents the header casing behavior.

Signed-off-by: Snow Pettersen <snowp@squareup.com>

Mirrored from https://github.com/envoyproxy/envoy @ 86420eb64a750fd6025cf5efc8b846c8fe63f0c9

envoy/api/v2/core/protocol.proto

@@ -74,8 +74,6 @@ message Http1ProtocolOptions {
 
   // Describes how the keys for response headers should be formatted. By default, all header keys
   // are lower cased.
-  // [#not-implemented-hide:] Hiding until both request and response formatting has been
-  // implemented.
   HeaderKeyFormat header_key_format = 4;
 }
 

envoy/api/v3alpha/core/protocol.proto

@@ -74,8 +74,6 @@ message Http1ProtocolOptions {
 
   // Describes how the keys for response headers should be formatted. By default, all header keys
   // are lower cased.
-  // [#not-implemented-hide:] Hiding until both request and response formatting has been
-  // implemented.
   HeaderKeyFormat header_key_format = 4;
 }