input: Write a python function to filter strings containing a specific pattern.
  assert filter_strings('aster', ["daisy", "sunflower", "asterisk", "cat", "monkey"]) == ["asterisk"]
  assert filter_strings('sun', ["daisy", "sunflower", "asterisk", "cat", "monkey"]) == ["sunflower"]
  assert filter_strings('cat', ["daisy", "sunflower", "asterisk", "cat", "monkey"]) == ["cat"]
  assert filter_strings('mon', ["daisy", "sunflower", "asterisk", "cat", "monkey"]) == ["monkey"]
output: def filter_strings(pattern, string_list):
      return [s for s in string_list if pattern in s]