[backport#16377 1/2][rpc] walletcreatefundedpsbt: don't automatically append inputs

Summary:
When the user doesn't specificy inputs, it makes sense to automatically select them. But when the user does specify inputs, we now fail if the amount is insufficient, unless addInputs is set to true.

Backport of Core PR16377 [1/2]

Test Plan:

ninja all check check-functional

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D8659