input: Write a function that takes a list of strings and returns the concatenation of all the elements with a separator/delimiter.
  def concatenate_strings(strings, separator):
   return separator.join(strings)
  
  assert concatenate_strings(["Sample","Text","Hello"], "/")=="Sample/Text/Hello"
  assert concatenate_strings(["Python","is","fun"], "-")=="Python-is-fun"
  assert concatenate_strings([""], ",")==""
  assert concatenate_strings(["a"], " ")=="a"
  assert concatenate_strings([], ":")==""
output: def concatenate_strings(strings, separator):
   return separator.join(strings)