[Feature Request] Change legend text height

### What is the feature?
Add a configuration method for `SeriesLabelStyle` to adjust the legend style to fit the paper article.
Currently, `SeriesLabelStyle` draws the legend with a `MultiLineText` object, and its default text height is 1.25.

```rust
chart
    .configure_series_labels()
    .legend_text_height(1.) // invoke `MultiLineText::set_line_height(f64)`
    .draw()?
```