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