:sparkles: Added custom holder for dragged elements

[mo-paralenz]

Added the ability to pass an element reference to SortableList to be used as a temporary container for dragged elements instead of using body.

When using CSS or SASS is very common to define component styles as children of some container, so when the dragged component gets moved to body all the styles get disabled.

// styles.scss
form {
  width: 100px;
  input {
    background: black;
    color: white;
    width: 50%;
  }
}

// MyComponent.(jsx|tsx)
const MyComponent = () => {
  const customHolderRef = useRef()

  return (
    <form>
      <div className="custom-holder" ref={customHolderRef} />
      <SortableList customHolderRef={customHolderRef} {...props}>
        {items.map((item) => (
          <SortableItem key={item}>
            <input type="text" value={item} />
          </SortableItem>
        ))}
      </SortableList>
    </form>
  )
}

This way the holder element for the dragged components can be located inside the same parent component as SortableList and keep all styles intact.

[ValentinH]

First of all, I'm sorry for the delay to review this PR. I've been quite busy recently. 😞

Then, thank you very much for this nice PR! I'm merging it now and will publish a new version.

[ValentinH]

Published as https://github.com/ValentinH/react-easy-sort/releases/tag/v1.5.0