input: Write a function called `concatenate_strings` that takes a list of strings and a separator/delimiter as parameters. The function should return the concatenation of all the elements in the list with the specified separator/delimiter.
  
  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([], " ") == ""
output: def concatenate_strings(strings, separator):
      return separator.join(strings)