input: Write a function to create a simple chatbot using Python and Dialogflow that can answer questions about the current days of the week. The function should set up a Flask app with a RESTful API, handle both GET and POST requests at the root route, and use Dialogflow to detect the intent of the user's text input. If a session ID is not present, the function should create one. The function should return the fulfillment text from Dialogflow as the response.
  
  assert create_chatbot()==
  This value is not applicable for assert since it is a setup function, but the chatbot should be able to answer questions about the days of the week accurately when tested with user input.
output: 
  def create_chatbot():
      from flask import Flask, request, jsonify
      import dialogflow
      import uuid
  
      app = Flask(__name__)
  
      @app.route('/', methods=['GET', 'POST'])
      def chat():
          user_input = request.args.get('text') if request.method == 'GET' else request.json.get('text')
          session_id = request.args.get('session_id') if request.method == 'GET' else request.json.get('session_id')
  
          if not session_id:
              session_id = str(uuid.uuid4())
  
          session_client = dialogflow.SessionsClient()
          session = session_client.session_path('YOUR_PROJECT_ID', session_id)
          text_input = dialogflow.types.TextInput(text=user_input, language_code='en-US')
          query_input = dialogflow.types.QueryInput(text=text_input)
          response = session_client.detect_intent(session=session, query_input=query_input)
  
          return jsonify({'response': response.query_result.fulfillment_text})
  
      return app
  