input: Write a python function to get the weekday name from a given date string.
  assert get_weekday('2020-01-01') == 'Wednesday'
  assert get_weekday('2023-10-10') == 'Tuesday'
  assert get_weekday('2023-01-01') == 'Sunday'
output: def get_weekday(date_string):
      import datetime
      date_obj = datetime.datetime.strptime(date_string, '%Y-%m-%d')
      return date_obj.strftime('%A')