Implement a per-chat message queue or similar for incoming messages

Currently (since 2.0.0b26), ETM is using a single message worker thread to process all incoming messages from the Bot admin in order to maintain a proper message order, and processing messages from slave channels on a per-call basis sent to Telegram.

While this former measure does help bring a proper message order, this is blocking all incoming messages in all chats when the worker is trying to process large (usually media) messages. This is obviously a behavior that we don‘t want to have in ETM. The latter is seemingly is not blocking, but this could result in a out-of-order message thread when a specific message needs to take more time than others.

I‘d like to look for help/suggestions to solve this problem by maintain a per-chat message order consistency while prevent blocking as far as possible. That could be a per-chat message queue or anything that could serve the same purpose.