Mongobridge nodes don't remember their network partition configuration after a restart

Mongobridge nodes allow us to partition the network between nodes in a replica set, but they don't store any durable state, so any of their current settings i.e. who they are dropping/accepting messages from, is lost when they are shut down and restart. This can be a problem for suites where we use mongobridges and also restart nodes i.e. rollback_fuzzer_unclean_shutdowns, Jepsen, etc., which may rely on a particular network topology being persistent across restarts.

There a few possible fixes for this. We could maintain a simple JSON configuration file that the mongobridge persists to disk and loads at restart, that stores the bridge's partitioning config. Alternatively, we could consider trying to keep a mongod's associated mongobridge running even when we shut down nodes in tests.