`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.
{
    const CChainParams& chainparams = Params();
    auto banman = std::make_unique<BanMan>(m_args.GetDataDirBase() / "banlist.dat", nullptr, DEFAULT_MISBEHAVING_BANTIME);
    auto connman = std::make_unique<CConnman>(0x1337, 0x1337, *m_node.addrman);
    auto peerLogic = PeerManager::make(chainparams, *connman, *m_node.addrman, banman.get(),
                                       *m_node.scheduler, *m_node.chainman, *m_node.mempool, false);
    banman->ClearBanned();
    int64_t nStartTime = GetTime();
    SetMockTime(nStartTime); 
    CAddress addr(ip(0xa0b0c001), NODE_NONE);
    CNode dummyNode(id++, NODE_NETWORK, INVALID_SOCKET, addr,  4,  4, CAddress(),  "", ConnectionType::INBOUND,  false);
    dummyNode.SetCommonVersion(PROTOCOL_VERSION);
    peerLogic->InitializeNode(&dummyNode);
    dummyNode.fSuccessfullyConnected = true;
    peerLogic->Misbehaving(dummyNode.GetId(), DISCOURAGEMENT_THRESHOLD,  "");
    {
        LOCK(dummyNode.cs_sendProcessing);
        BOOST_CHECK(peerLogic->SendMessages(&dummyNode));
    }
    BOOST_CHECK(banman->IsDiscouraged(addr));
    peerLogic->FinalizeNode(dummyNode);
}
class TxOrphanageTest : public TxOrphanage