Cardano Staking: support MaxAmount for staking as well

[optout21]

Is your feature request related to a problem? Please describe. For 'simple' Cardano transfer, UseMaxAmount option can be set to achieve sending all available funds (all avail minus fee). For staking this is not possible.

Describe the solution you'd like For staking, allow setting the UseMaxAmount option: if set, take all available funds, subtract the deposit and fee, and include all remaining in staking amount.

Describe alternatives you've considered

Additional context

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