Integrate real time GDP growth

• Web page: https://www.oecd.org/economy/weekly-tracker-of-gdp-growth/
• Git repository: https://github.com/NicolasWoloszko/OECD-Weekly-Tracker
• Raw data: https://github.com/NicolasWoloszko/OECD-Weekly-Tracker/raw/main/Data/weekly_tracker.xlsx
• Create a new dataset with code GDP_GROWTH and name "Weekly tracker of economic activity (GDP growth)" and add it to the (flat) category tree of the OECD provider