earthobservations/wetterdienst: Fix InfluxDB exports and increase efficiency and performance

Abstract

InfluxDB export: Fix export in non-tidy format (#230). Thanks, @wetterfrosch! InfluxDB export: Use "quality" column as tag (#234). Thanks, @wetterfrosch! InfluxDB export: Use a batch size of 50000 to handle larger amounts of data (#235). Thanks, @wetterfrosch! Update radar examples to use wradlib>=1.9.0. Thanks, @kmuehlbauer! Change wherever possible column type to category Increase efficiency by downloading only historical files with overlapping dates if start_date and end_date are given Use periods dynamically depending on start and end date Fix inconsistency within 1 minute precipitation data where historical files have more columns Improve DWD PDF parser to extract quality information and select language. Also, add an example at example/dwd_describe_fields.py as well as respective documentation