`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.
assert(!node.connman);
    node.connman = std::make_unique<CConnman>(GetRand(std::numeric_limits<uint64_t>::max()), GetRand(std::numeric_limits<uint64_t>::max()), *node.addrman, args.GetBoolArg("-networkactive", true));
    assert(!node.fee_estimator);
    
    
    if (!ignores_incoming_txs) node.fee_estimator = std::make_unique<CBlockPolicyEstimator>();
    assert(!node.mempool);
    int check_ratio = std::min<int>(std::max<int>(args.GetArg("-checkmempool", chainparams.DefaultConsistencyChecks() ? 1 : 0), 0), 1000000);
    node.mempool = std::make_unique<CTxMemPool>(node.fee_estimator.get(), check_ratio);
    assert(!node.chainman);
    node.chainman = std::make_unique<ChainstateManager>();
    ChainstateManager& chainman = *node.chainman;
    assert(!node.peerman);
    node.peerman = PeerManager::make(chainparams, *node.connman, *node.addrman, node.banman.get(),
                                     *node.scheduler, chainman, *node.mempool, ignores_incoming_txs);
    RegisterValidationInterface(node.peerman.get());
    
    std::vector<std::string> uacomments;
    for (const std::string& cmt : args.GetArgs("-uacomment")) {
        if (cmt != SanitizeString(cmt, SAFE_CHARS_UA_COMMENT))
            return InitError(strprintf(_("User Agent comment (%s) contains unsafe characters."), cmt));
        uacomments.push_back(cmt);
    }
    strSubVersion = FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, uacomments);
    if (strSubVersion.size() > MAX_SUBVERSION_LENGTH) {
        return InitError(strprintf(_("Total length of network version string (%i) exceeds maximum length (%i). Reduce the number or size of uacomments."),
            strSubVersion.size(), MAX_SUBVERSION_LENGTH));
    }
    if (args.IsArgSet("-onlynet")) {
        std::set<enum Network> nets;