input: Write a python function to categorize text into positive, negative, or neutral.
  assert categorize_text("I am very happy today!") == "positive"
  assert categorize_text("This is such a sad moment.") == "negative"
  assert categorize_text("It's a regular day.") == "neutral"
output: def categorize_text(text):
      positive_keywords = ["happy", "joy", "love", "excited", "fantastic", "great"]
      negative_keywords = ["sad", "angry", "hate", "upset", "terrible", "bad"]
      
      text_lower = text.lower()
      
      for word in positive_keywords:
          if word in text_lower:
              return "positive"
      
      for word in negative_keywords:
          if word in text_lower:
              return "negative"
      
      return "neutral"