Resolve "release v2.4.0"

Closes #458

See merge request !521

filter can now combine obs, forecast, and apriori for first iteration. Further...

See merge request !522

Resolve "set config paths as parameter"

See merge request !520

Resolve "load ifs data"

See merge request !517

# Conflicts:
#   mlair/data_handler/data_handler_single_station.py

Resolve "Use Toar statistics api v2"

See merge request !518

Resolve "advanced retry strategy"

See merge request !516

filter can now combine obs, forecast, and apriori for first iteration. Further adjustments are required

Merge branch 'lukas_issue453_refac_advanced-retry-strategy' into michael_issue450_feat_load-ifs-data

Resolve "update proj version"

See merge request !515

Resolve "load era5 data from toar db"

See merge request !514

Resolve "robust apriori estimate for short timeseries"

See merge request !513