When an event is created and there's a subscriber attached to the topic, only the current instance runs the function.
This is ideal, when we want to react to the event only once - for example: "Entity status change sends a notification".

When Ayon is scaled (there are multiple instances of the server itself), we also need a way how to trigger the function on all instances.
For example "Settings of the addon changed, so all addon instances has to reload the cache".

Proposal:

Add another parameter all_nodes: bool (defaulting to False) to EventStream.subscribe method.
When set to True, the function will be triggered on all instances of the server.

Implementation:

Hooks need to be split to groups (all / current node). Implementation for current node remains the same,
while all_nodes require implementation in ayon_server.api.messaging