granular network control

I've mentioned this on cabal a bit already, but it would be great if the cabal clients had more granular control over their connections. In some situations you might want to turn off all connections to save battery or bandwidth. In others you might only want local MDNS but not the public internet. In others you might not want to broadcast over MDNS for privacy. Making these settings configurable at runtime and showing a prompt when first running about the considerations around each type of connection would be very helpful.

No files or tests are named. Start by locating the Cabal client connection-management and first-run prompt entry points, then determine how runtime settings can distinguish all connections, local mDNS, and public internet access. Done means the requested connection modes are configurable and the startup prompt explains their trade-offs.

Written by the indexing model from the issue text.