Implement configuration reference generation

[ftsell]

In my opinion there should be a way to automatically generate a configuration reference for my Django project when using django-configurations so that I can easily include it in project documentation without just referencing some source file.

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I was thinking of a workflow like the following:

from configurations import Configuration, values

class MyConfiguration(Configuration):
    DEBUG = values.BooleanValue(default=True)
    SECRET_KEY = values.SecretValue(description="The django secret key", reference="https://docs.djangoproject.com/en/3.0/ref/settings/#std:setting-SECRET_KEY")
    IS_AWESOME_FEATURE_ENABLED = values.BooleanValue(description="Enables the awesome feature because of which you want to run this application")

manage.py create-configuration-reference --format github-markdown-table --out ./configuration-reference.md

Key | Type | Default | Description
--- | --- | --- | ---
DEBUG | [bool](https://django-configurations.readthedocs.io/en/stable/values/#configurations.values.BooleanValue) | True |
SECRET_KEY | [secret](https://django-configurations.readthedocs.io/en/stable/values/#configurations.values.SecretValue) | *not set* | [reference](https://docs.djangoproject.com/en/3.0/ref/settings/#std:setting-SECRET_KEY): The django secret key
IS_AWESOME_FEATURE_ENABLED | [bool](https://django-configurations.readthedocs.io/en/stable/values/#configurations.values.BooleanValue) | *not set* | Enables the awesome feature because of which you want to run this application

Which renders as

Key	Type	Default	Description
DEBUG	bool	True
SECRET_KEY	secret	not set	reference: The django secret key
IS_AWESOME_FEATURE_ENABLED	bool	not set	Enables the awesome feature because of which you want to run this application

---

I am willing to implement and maintain this feature if it is desired.
I am also open for discussions about the details.