Is there a way to specify the absolute fee of a transaction?

[ValuedMammal]

Additional Context

bitcoindevkit/bdk_wallet#297 (comment)

I think a straightforward approach is to set a target feerate of 0 and add the fee amount to the output value_sum. The effect is to raise the cost of meeting the target by the amount of the target fee.

[aagbotemi]

Yes, we can add the absolute_fee field to SelectorParams, and from the target_outputs we can add the absolute fee to the value_sum, then we can set the target_feerate to ZERO