`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.
static const bool DEFAULT_REST_ENABLE = false;
#ifdef WIN32
#define MIN_CORE_FILEDESCRIPTORS 0
#else
#define MIN_CORE_FILEDESCRIPTORS 150
#endif
static const char* DEFAULT_ASMAP_FILENAME="ip_asn.map";
/**
 * The PID file facilities.
 */
static const char* BITCOIN_PID_FILENAME = "bitcoind.pid";
static fs::path GetPidFile(const ArgsManager& args)
{
    return AbsPathForConfigVal(fs::path(args.GetArg("-pid", BITCOIN_PID_FILENAME)));
}
[[nodiscard]] static bool CreatePidFile(const ArgsManager& args)
{
    fsbridge::ofstream file{GetPidFile(args)};
    if (file) {
#ifdef WIN32
        tfm::format(file, "%d\n", GetCurrentProcessId());
#else
        tfm::format(file, "%d\n", getpid());
#endif
        return true;
    } else {
        return InitError(strprintf(_("Unable to create the PID file '%s': %s"), GetPidFile(args).string(), std::strerror(errno)));
    }
}
void Interrupt(NodeContext& node)