`banlist.dat` was introduced in https://github.com/bitcoin/bitcoin/pull/6310, storing nodes that were automatically banned (due to exceeding the misbehavior threshold) and manually banned (through the `setban` RPC).

Automatic bans were removed in https://github.com/bitcoin/bitcoin/pull/19219 and replaced with a discouragement filter. That filter is not saved to disk/persisted over shutdown/startup. The `banlist.dat` therefore now only contains addresses that have been banned through the `setban` rpc.

Since https://github.com/bitcoin/bitcoin/pull/15935, we have a specific file for configuration that is updated through the RPC and persisted over shutdown/startup, namely `settings.json`. We should therefore move the manual ban configuration from `banlist.dat` to `settings.json`. Doing so has a couple of benefits:

- `settings.json` is human readable and easily analyzable by any json parser.
- we wouldn't need to maintain custom [de]serialization code for the `banlist.dat` file.

`banlist.dat` is expected to be fairly small and infrequently updated, so disk space/performance are not huge concerns.
for (const std::string& snet : args.GetArgs("-onlynet")) {
            enum Network net = ParseNetwork(snet);
            if (net == NET_UNROUTABLE)
                return InitError(strprintf(_("Unknown network specified in -onlynet: '%s'"), snet));
            nets.insert(net);
        }
        for (int n = 0; n < NET_MAX; n++) {
            enum Network net = (enum Network)n;
            if (!nets.count(net))
                SetReachable(net, false);
        }
    }
    
    fNameLookup = args.GetBoolArg("-dns", DEFAULT_NAME_LOOKUP);
    bool proxyRandomize = args.GetBoolArg("-proxyrandomize", DEFAULT_PROXYRANDOMIZE);
    
    
    std::string proxyArg = args.GetArg("-proxy", "");
    SetReachable(NET_ONION, false);
    if (proxyArg != "" && proxyArg != "0") {
        CService proxyAddr;
        if (!Lookup(proxyArg, proxyAddr, 9050, fNameLookup)) {
            return InitError(strprintf(_("Invalid -proxy address or hostname: '%s'"), proxyArg));
        }
        proxyType addrProxy = proxyType(proxyAddr, proxyRandomize);
        if (!addrProxy.IsValid())