Send MAX button for sweeping a wallet's balance.

[pacu]

Is your feature request related to a problem? Please describe.

I'm always frustrated when I need to send my max balance to some other wallet.

Describe the solution you'd like

I'd like to just hit a send max button and that fees and max amount are determined by the wallet.

Alternatives you've considered

I've been using the calculator 😂

Additional context

I'm actually sending my sapling testnet funds to orchard by sending the max amount to the UA. Obviously this is not convenient in terms fo privacy. But this also applies to people sweeping a shielded wallet without jumping pools and revealing funds.

It would nice that the fee is discriminated from the amount in the Error message so it's more useful to the user.