Sponsor sBTC transfers

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Sending sBTC (or any SIP010 token) while no STX is available fails with "Not enough funds" (Not enough STX/gas, would be a more helpful error here)

This could be a short term fix, while we work on sponsoring such a transaction instead when insufficient STX funds are available.

[linear]

LEA-2688 Improve error message "Not enough funds" to "Not enough STX/gas funds"