public int http2InitialConnectionWindowSize() {
        return get(HTTP2_INITIAL_CONNECTION_WINDOW_SIZE);
    }
Returns the HTTP/2 <a href="https://datatracker.ietf.org/doc/html/rfc7540#section-6.9.2">initial connection
flow-control window size</a>.
core/src/main/java/com/linecorp/armeria/client/ClientFactoryOptions.java