input: Write a python function to find strings that start with the same letter in a given list of strings.
  assert find_same_letter_substrings(['apple', 'mango', 'carrot', 'dog']) == ['apple', 'mango', 'carrot']
  assert find_same_letter_substrings(['banana', 'berry', 'cherry', 'chocolate']) == ['banana', 'berry', 'cherry', 'chocolate']
  assert find_same_letter_substrings(['ant', 'bee', 'cat', 'dog', 'elephant']) == []
output: def find_same_letter_substrings(strings):
      result = []
      if not strings:
          return result
  
      first_letter = strings[0][0]
      for string in strings:
          if string[0] == first_letter:
              result.append(string)
          else:
              break
  
      return result