chore: update translation for first day of week

Added translation connected to: https://github.com/frappe/frappe/pull/15669

frappe/translations/de.csv

@@ -91,6 +91,7 @@ Field Name,Feldname,
 Fieldname,Feldname,
 Fields,Felder,
 First Name,Vorname,
+First Day of the Week,Erster Wochentag,
 Frequency,Häufigkeit,
 Friday,Freitag,
 From,Von,