Automatic reference to configuration reference docs

Hello, I would like it to be possible to easily refer to the reference list with configuration options. Currently, most of the guides that require a description of configuration options are similar to the description below. <img width="941" alt="Screenshot 2020-08-09 at 13 48 55" src="https://user-images.githubusercontent.com/12058428/89731407-177fb500-da47-11ea-9df5-8a17b910da35.png"> There are code literals in this text: ``backend``, ``[secrets]``. Unfortunately, these literals are just text and I wish they could be clicked to go to a reference list containing a description of the option/section. To do this, we should add a new reference type, make changes to [the listing template](https://github.com/apache/airflow/blob/master/docs/configurations-ref.rst), and then make changes to all descriptions. We can be inspired by the Django project. https://github.com/django/django/blob/58a336a674a658c1cda6707fe1cacb56aaed3008/docs/_ext/djangodocs.py#L47-L52 Best regards, Kamil Breguła