input: Write a function named `create_flask_app` that creates a Flask web application which takes user input and generates an HTML page displaying the input. The function should return the Flask app instance. The HTML template for displaying the input should be named 'result.html' and the initial page should be named 'index.html'.
  
  assert create_flask_app().name == 'Flask'
  assert create_flask_app().template_folder == 'templates'
output: from flask import Flask, render_template, request
  
  def create_flask_app():
      app = Flask(__name__)
  
      @app.route('/')
      def index():
          return render_template('index.html')
  
      @app.route('/result', methods=['POST'])
      def result():
          user_input = request.form['user_input']
          return render_template('result.html', user_input=user_input)
  
      return app