gui: bumpfee signer support
gui: bumpfee signer support

Specifically this enables the Send button in the fee bump dialog for wallets with external signer support. Similar to 2efdfb88aab6496dcf2b98e0de30635bc6bade85.

Github-Pull: #21576
Rebased-From: 2c07cfacd1745844a1d3c57f2e8617549b9815d7

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