input: Write a function that takes a list of strings and a separator/delimiter as parameters and returns the concatenation of all the elements with the specified separator. If the list is empty, return an empty string.
  assert concatenate_strings(["Sample","Text","Hello"], " - ")=="Sample - Text - Hello"
  assert concatenate_strings(["Hello","World"], ",")=="Hello,World"
  assert concatenate_strings([], "-")==""
  assert concatenate_strings(["Python"], ".")=="Python"
  assert concatenate_strings(["Code","Debug","Test"], ":")=="Code:Debug:Test"
output: def concatenate_strings(strings, separator):
      if not strings:
          return ""
      return separator.join(strings)