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. 
* ReserveDestination is used to reserve an address.
 * It is currently only used inside of CreateTransaction.
 *
 * Instantiating a ReserveDestination does not reserve an address. To do so,
 * GetReservedDestination() needs to be called on the object. Once an address has been
 * reserved, call KeepDestination() on the ReserveDestination object to make sure it is not
 * returned. Call ReturnDestination() to return the address so it can be re-used (for
 * example, if the address was used in a new transaction
 * and that transaction was not completed and needed to be aborted).
 *
 * If an address is reserved and KeepDestination() is not called, then the address will be
 * returned when the ReserveDestination goes out of scope.
 */
class ReserveDestination
{
protected:
    
    const CWallet* const pwallet;
    
    ScriptPubKeyMan* m_spk_man{nullptr};
    OutputType const type;
    
    int64_t nIndex{-1};
    
    CTxDestination address;
    
    bool fInternal{false};
public:
    
    explicit ReserveDestination(CWallet* pwallet, OutputType type)