Dynamic network connections

Currently, network connection are set up based on roster on startup of the application. To allow Dynamic Address Book, we need to support tearing down and setting up completely new connections during runtime. This will also help for possible future use cases involving more complex protocols, utilising not fully connected graphs.

This epic covers all the changes related to supporting dynamic connections, communicating them to network layer, handling concurrent access for connection changes. It does NOT cover way of agreeing on new address books between the nodes, communicating roster changes between the nodes or handling them on the shadowgraph or consensus level.

No files, tests, or entry points are identified. Start by tracing how the roster creates connections during application startup, then map the network-layer changes needed for runtime teardown, setup, and concurrent connection updates. Done means dynamic connection changes work without addressing roster agreement, inter-node roster communication, shadowgraph handling, or consensus changes.

Written by the indexing model from the issue text.