FundPsbt and EstimateFee improvements

[jalavosus]

FundPsbt and EstimateFee now support spending from the underlying
wallet using unconfirmed inputs or inputs with a specific number of
minumum confirmations; this is made possible by adding the
params min_confs and spend_unconfirmed to the underlying proto
messages, and implementing checks in their function calls.

This commit also changes the interface of WalletController slightly; it
adds the param minConfs to CreateSimpleTx inside the
WalletController interface, thus allowing the underlying
implementation of the function to pass minConfs to its
underlying wallet's createsimpletx implementation (if possible and/or desired).

Pull Request Checklist

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[guggero]

@jalavosus was the repo for this PR removed by accident? Or what happened?
Was going to review this now, since 0.12.0 is almost out. Or should I instead close this and review #4905?

[jakesylvestre]

@jalavosus I went ahead and applied the patch for this commit to xplorfin#11 so if you want to change the base branch to xplorfin/fundpsbt we should be good to go here

[Roasbeef]

We should either proceed with this or #4905

[guggero]

Closing this due to inactivity and in favor of #4905.