Networked message brokers

[ehpor]

Caution

This PR requires #331 and #342 to be merged before.

This PR adds a message broker that allows access to message brokers over the network. This allows other computers to talk to you using a consistent interface.

Todo:

• Rename MessageBroker to LocalMessageBroker.
• Separate out a MessageBroker interface.
• Write a RemoteMessageBroker that connects to other RemoteMessageBroker objects via the network.
• Write a DistributedMessageBroker class that distributes messages between a LocalMessageBroker and a RemoteMessageBroker depending on the prefix of the message topic.

[a-sevin]

Hi,
I spent a few dozen hours of my nights and weekends continuing the development work.
I have a proof of concept using a remote camera server that sends frames to the main testbed.
I need some time to validate the various test cases (such as services not started or crashed), but the first tests are successful.
I’ve pushed everything to the branch message_networking_v2.
I’m not sure whether I should create a new PR or push to this one.
DISTRIBUTED_MESSAGING.md was generated by Copilot, so it may contain errors... Now, I need some rest

[ehpor]

@a-sevin Amazing! I'm very grateful for your work on this.

One concern that I hadn't solved yet was that we don't want to send every message to all computers. Cameras generate a lot of bandwidth, and we don't want to send all that data to a computer just for it to be ignored since it's just handling flip mounts or something. We want to be selective.

Another thing that I ran into, that you seem to have spent a lot of time on, is service process management. My approach was gonna be to do all communication via the message broker, and have it serve as the only communication line between the two computers. You're still using some ZeroMQ there?

That being said, this is a great work!