text: Title: Option for execute_notebook() to disable expansion of parameters in the input path
  Body: Dear papermilll maintainers,
  
  Is it possible to have an option for execute_notebook(), which disables expansion of parameters in the source path?
  
  I am using parameters in the file name to automatically produce multiple reports stemming from the same source notebook, e.g.:
  
  ```
  papermill.execute_notebook('{param}/notebook.ipynb', 'value1/notebook.ipynb',
                                  parameters={'param': 'value1'})
  papermill.execute_notebook('{param}/notebook.ipynb', 'value2/notebook.ipynb',
                                  parameters={'param': 'value2'})
  ```
                                  
  I cannot use this pattern with the current version of papermill, because it expands the input notebook name producing:
  
  ```
  value1/notebook.ipynb -> value1/notebook.ipynb 
  value2/notebook.ipynb -> value2/notebook.ipynb 
  ```
  
  This fails because the source notebook does not exists.
  
  I'd like to have all target reports produced from the single template notebook, which includes parameters in the path:
  ```
  {param}/notebook.ipynb -> value1/notebook.ipynb 
  {param}/notebook.ipynb -> value2/notebook.ipynb 
  ```
  
  I cannot do it, because papermill expands parameters in both source and target file.
  
  My suggestion is to introduce a bool option _parametrize_input_path_ in _execute_notebook()_, which disables expansion of parameters in the source path, like:
  
  ```
  papermill.execute_notebook('{param}/notebook.ipynb', 'value1/notebook.ipynb',
                                  parameters={'param': 'value1'}, 
                                  parametrize_input_path=False)
  ```
  
  I include suggested PR to the issue.
  
  Kind regards,
  Anton