Since #13666 our fee calculation assumes that ECSDA signatures are a maximum of 71 bytes, rather than 72. However, not all hardware wallets implement R-value grinding.

This can cause us to underpay fees when using an external signer. That's especially problematic when the user picks 1 sat/vbyte as the fee, because it won't even get into our own mempool.

The easiest solution would be to modify `ExternalSignerScriptPubKeyMan` to assume 72 bytes for ECSDA signatures.

Slightly more advanced would be to expand HWI to keep track of which devices and firmware versions (if any) support R-value grinding. We'd then have to store that in the wallet in some new field. Personally I'd rather work on better Taproot support, which thanks to Schnorr avoids this issue altogether. 
size_t* n_signed = nullptr,
                  bool finalize = true) const;
    /**
     * Submit the transaction to the node's mempool and then relay to peers.
     * Should be called after CreateTransaction unless you want to abort
     * broadcasting the transaction.
     *
     * @param[in] tx The transaction to be broadcast.
     * @param[in] mapValue key-values to be set on the transaction.
     * @param[in] orderForm BIP 70 / BIP 21 order form details to be set on the transaction.
     */
    void CommitTransaction(CTransactionRef tx, mapValue_t mapValue, std::vector<std::pair<std::string, std::string>> orderForm);
    
    bool SubmitTxMemoryPoolAndRelay(CWalletTx& wtx, std::string& err_string, bool relay) const
        EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    bool DummySignTx(CMutableTransaction &txNew, const std::set<CTxOut> &txouts, const CCoinControl* coin_control = nullptr) const
    {
        std::vector<CTxOut> v_txouts(txouts.size());
        std::copy(txouts.begin(), txouts.end(), v_txouts.begin());
        return DummySignTx(txNew, v_txouts, coin_control);
    }
    bool DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut> &txouts, const CCoinControl* coin_control = nullptr) const;
    bool ImportScripts(const std::set<CScript> scripts, int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    bool ImportPrivKeys(const std::map<CKeyID, CKey>& privkey_map, const int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    bool ImportPubKeys(const std::vector<CKeyID>& ordered_pubkeys, const std::map<CKeyID, CPubKey>& pubkey_map, const std::map<CKeyID, std::pair<CPubKey, KeyOriginInfo>>& key_origins, const bool add_keypool, const bool internal, const int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    bool ImportScriptPubKeys(const std::string& label, const std::set<CScript>& script_pub_keys, const bool have_solving_data, const bool apply_label, const int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    CFeeRate m_pay_tx_fee{DEFAULT_PAY_TX_FEE};
    unsigned int m_confirm_target{DEFAULT_TX_CONFIRM_TARGET};
    /** Allow Coin Selection to pick unconfirmed UTXOs that were sent from our own wallet if it
     * cannot fund the transaction otherwise. */