text: Title: [ENH] expose fitted parameters of `AutoETS` via `get_fitted_params`
  Body: The fitted parameters of `AutoETS` should be visible via `get_fitted_params`.
  
  For this, at the end of `_fit`, we need to write the attributes we want to be visible to `self.paramname_`, ending in an underscore.
  
  @ericjb has already found some parameters that we could write, though I am not certain about whether there are more, see here: https://github.com/sktime/sktime/discussions/7184
  
  FYI @ericjb 