protected final void setGoAwayDebugMessage(String debugMessage) {
        goAwayDebugData = Unpooled.unreleasableBuffer(
                Unpooled.copiedBuffer(debugMessage, StandardCharsets.UTF_8));
    }
Sends a {@code GO_AWAY} frame to initiate connection shutdown. No-op if channel isn't active.
Does <strong>not</strong> flush immediately, this is the responsibility of the caller.
core/src/main/java/com/linecorp/armeria/internal/common/AbstractHttp2ConnectionHandler.java