input: Write a python function to convert a given timestamp to UTC time in the format '%Y-%m-%d %H:%M:%S'.
  assert convert_to_utc(1594842400) == '2020-07-17 02:00:00'
  assert convert_to_utc(1609459200) == '2021-01-01 00:00:00'
  assert convert_to_utc(1622505600) == '2021-06-01 00:00:00'
output: def convert_to_utc(timestamp):
      from datetime import datetime, timezone
      utc_time = datetime.fromtimestamp(timestamp, timezone.utc)
      return utc_time.strftime('%Y-%m-%d %H:%M:%S')