[Feature] Add option for dynamically calculated label position for bar type

### What problem does this feature solve?

Currently there is no way of showing labels inside or outside of bars depending on their size. This leads to the following:


If there was an option to return label properties dynamically it could help make it more visually appealing.

### What does the proposed API look like?

add a function type option for the [position property in label](https://echarts.apache.org/en/option.html#series-bar.label.position)

position: (bar: RectLike, textRect: RectLike, text: string) =>

having the bar rect and the the textRect will allow the user to do any calculations desired in order to decide the final position of the label