Enhance BarChartDataset and DataLabels documentation

Updated the `BarChartDataset` class to include new properties with detailed descriptions, default values, and versioning attributes. Key properties added include `BackgroundColor`, `BarPercentage`, `BarThickness`, and more, all with comprehensive XML documentation.

Modified the `BarChartDatasetDataLabels` class to introduce new properties for data label configuration, including `Alignment` and `Anchor`, along with enhancements for `DataLabelsAlignment` and `DataLabelsAnchor`. These changes improve usability and clarity for developers.

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Author: gvreddy04