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