input: Write a python function to create a simple Flask application with a homepage that renders an HTML template.
  assert create_flask_app().url_map == app.url_map
  assert create_flask_app().view_functions['homepage']() == render_template('homepage.html')
output: def create_flask_app():
      from flask import Flask, render_template
      
      app = Flask(__name__)
      
      @app.route('/')
      def homepage():
          return render_template('homepage.html')
      
      return app