Creation of data_statistics.csv file is missing

[LevanBokeria]

The 03-update_data_statistics.py script expects a data_statistics.csv file to exist in the data directory. However, this file is not created by any code, including the 02-fetch_gbif_moth_data.py.

Proposed solution is to check if data_statistics.csv file already exists. If so, then load it. If not, create an empty dataframe with the right columns. I will create a PR with a suggested solution.