text: Title: Add function get_value to FSMContext
  Body: ### aiogram version
  
  3.x
  
  ### Problem
  
  In a situation where you only need to take one value in FSMContext handler, you need to write 2 lines of code to take value
  
  ### Possible solution
  
  Add a get_value function for FSMContext that takes value by key
  
  ### Alternatives
  
  _No response_
  
  ### Code example
  
  ```python3
  # before
  data = await state.get_data()
  name = data["name"]
  
  # after
  name = await state.get_value("name")
  ```
  
  
  ### Additional information
  
  _No response_