Integrate holiday data

[markus-dus]

Using the file school_holiday_data_2014_2024.csv we have an issue with duplicates: "2021-01-26" and a couple of other dates have two entries. public holidays look fine, though.

[mebrahimkhas]

The duplicated data in school_holiday_data_2014_2024.csv has been solved. the reason for duplicated some of date was the following: I used two sources to get the data, now there is not duplicated data

[markus-dus]

nice - looks good now