Feature request: Add a setting for Default Withdrawal max fee

[cointastical]

For withdraw from an account on SN, the 10 sats (default) is a higher amount than is needed for most any transaction amount that would be typically withdrawn from SN.

This request is to add to /settings a: Default Withdrawal max fee.

That value then would be the value that is used to prefill the max fee field in /withdraw.

So if having Default Withdrawal max fee set to 1 sats, most withdrawal attempts will likely succeed. If, for whatever reason, that withdraw fail, the user can then try again but raise the max fee a little higher on the next attempt.

The initial value for a new account on SN (for the Default Withdrawal max fee) could remain 10 sats, ... just that this setting gives users the option to customize that value so that they no longer need to edit the max fee when performing each withdrawal.