input: Write a function to create a web application using Flask that takes user input and generates an HTML page with the input displayed. If the input is not provided, it should display a default message. 
  
  assert create_flask_app('Hello world')=='<h1>Your Input: </h1>\n  <p>Hello world</p>'
  assert create_flask_app('')=='<h1>Your Input: </h1>\n  <p>No input provided</p>'
  assert create_flask_app(None)=='<h1>Your Input: </h1>\n  <p>No input provided</p>'
output: def create_flask_app(user_input):
      if not user_input:
          return '<h1>Your Input: </h1>\n  <p>No input provided</p>'
      return f'<h1>Your Input: </h1>\n  <p>{user_input}</p>'