buffer size: expand response buffer limit to 1Mb

[junr03]

Description: expands the buffer size of the DirectStream from 65kb to 1mb.
Risk Level: low - previously responses reaching the limit size would have resulted in an error.
Testing: tested with the example apps and this Envoy diff

diff --git a/source/common/http/filter_manager.cc b/source/common/http/filter_manager.cc
index 2864da7758..ec102fa515 100644
--- a/source/common/http/filter_manager.cc
+++ b/source/common/http/filter_manager.cc
@@ -1531,6 +1531,7 @@ Buffer::InstancePtr ActiveStreamEncoderFilter::createBuffer() {
       [this]() -> void { this->responseDataDrained(); },
       [this]() -> void { this->responseDataTooLarge(); },
       []() -> void { /* TODO(adisuissa): Handle overflow watermark */ });
+  ENVOY_LOG_MISC(error, "setting buffer limit {}", parent_.buffer_limit_);
   buffer->setWatermarks(parent_.buffer_limit_);
   return buffer;
 }

[junr03]

@alyssawilk you were totally right about #1934 (comment). The true origin of that buffer limit is the DirectStream in Envoy Mobile. This PR increases the limit to 1mb for now, I have created #1988 to make the setting configurable.

I followed the response_payload_too_large message to the filter manager where the local response is sent, and from there to where responseDataTooLarge() is used. And then used the log above to see the value.

[buildbreaker]

Nice