fix: test proxy doesn't return "http2 excpetion" for long errors (#2775)

Co-authored-by: Patrick Wrobel <pwrobel@google.com>

Author: PeteyPii

test-proxy/src/main/java/com/google/cloud/bigtable/testproxy/CbtTestProxy.java

@@ -828,6 +828,9 @@ private InstantiatingGrpcChannelProvider getTransportChannel(
               public ManagedChannelBuilder apply(ManagedChannelBuilder input) {
                 NettyChannelBuilder channelBuilder = (NettyChannelBuilder) input;
 
+                // The default replaces long (several KiB) error messages with "http2 exception"
+                channelBuilder.maxInboundMetadataSize(Integer.MAX_VALUE);
+
                 if (sslContext != null) {
                   channelBuilder.sslContext(sslContext);
                 }