feat: allow custom input element override for DatePicker

[karrui]

allows for users to trigger the calendar without using the default input

A little convoluted to use, but allows the flexibility if needed!

Example usage

// Custom input
// !!REQUIRES `forwardRef` to be set so Popover parent knows where to anchor to.
const CustomInputButton = forwardRef<object, 'button'>((_props, ref) => {
  const { inputRef, innerRef, disclosureProps: { onOpen } } = useDatePicker()
  // !!Important to use forwarded ref so popover knows where to anchor to
  const refs = useMergeRefs(inputRef, innerRef, ref)

  return (
    <Button ref={refs} onClick={onOpen}>
      please look at source code to see how to use custom elements
    </Button>
  )
})

// Usage
<DatePicker inputElement={<CustomInputButton />} {...restOfProps} />