disable response buffering on the websocket

Jersey buffers responses (by default up to 8192 bytes) just so it can
add a content length to responses. We already buffer our responses to
serialize them as protos, so we can compute the content length
ourselves. Setting the buffer to zero disables buffering.

websocket-resources/src/test/java/org/whispersystems/websocket/WebSocketResourceProviderTest.java

@@ -137,6 +137,7 @@ class WebSocketResourceProviderTest {
         return "OK";
       }
     });
+    when(response.getHeaders()).thenReturn(new MultivaluedHashMap<>());
 
     ArgumentCaptor<OutputStream> responseOutputStream = ArgumentCaptor.forClass(OutputStream.class);