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. 
// ensure this wal.dat can only be opened by clients supporting HD with chain split and expects no default key
        walInstance->SetMinVersion(FEATURE_LATEST);
        walInstance->InitWalFlags(wal_creation_flags);
        // Only create LegacyScriptPubKeyMan when not  wal
        if (!walInstance->IsWalFlagSet(WALLET_FLAG_DESCRIPTORS)) {
            walInstance->SetupLegacyScriptPubKeyMan();
        }
        if ((wal_creation_flags & WALLET_FLAG_EXTERNAL_SIGNER) || !(wal_creation_flags & (WALLET_FLAG_DISABLE_PRIVATE_KEYS | WALLET_FLAG_BLANK_WALLET))) {
            LOCK(walInstance->cs_wal);
            if (walInstance->IsWalFlagSet(WALLET_FLAG_DESCRIPTORS)) {
                walInstance->SetupDescriptorScriptPubKeyMans();
                // SetupDe
            } else {
                // Legacy 
                for (auto spk_man  walInstance->GetActiveScriptPubKeyMans()) {
                    if (!spk_man->SetupGeneration()) {
                        error = _("Unable to generate initial keys");
                        return nullptr;
                    }
                }
            }
        }
        if (chain) {
            walInstance->chainStateFlushed(chain->getTipLocator());
        }
    } else if (wal_creation_flags & WALLET_FLAG_DISABLE_PRIVATE_KEYS) {
        // Make it impossible to disable private keys after creation
        error = strprintf(_("Error loading %s Private keys can only be disabled during creation"), walFile);
        return nullptr;
    } else if (walInstance->IsWalFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {