feat: Use a FieldGroup to add the euro unit

[ptbrowne]

The amount field in the transfer wizard did not have a unit.

[todo]

remove if cozy/cozy-ui#1113 is merged

cozy-banks/src/ducks/transfers/steps/Amount.jsx

Lines 32 to 37 in 9f781d1

	// TODO remove if https://github.com/cozy/cozy-ui/pull/1113 is merged
	const InputGroupUnit = ({ children }) => (
	<Bold className="u-ph-1">{children}</Bold>
	)
	class _ChooseAmount extends React.PureComponent {

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This comment was generated by todo based on a TODO comment in 9f781d1 in #1430. cc @cozy.