Add a method to mark settings as sensitive with patterns

[grimmy]

There should be a way to make settings sensitive, so that I can get a userfacing copy of them without giving out secrets. For example, so I have something like:

OAUTH2_PROVIDER_TOKEN: 'abc3b45b2b2b6b89099987399bacdfe23fde'

I would like to know that the key exists to show it on a health endpoint or some other mechanism to verify that it's configured. I was thinking something like:

@sensitive
OAUTH2_PROVIDER_TOKEN: 'abc3b45b2b2b6b89099987399bacdfe23fde'

and then something like this would work.

 >>> import settings
 >>> print(settings.OAUTH2_PROVIDER_TOKEN)
 **************

However, I also have settings that are uris, so I need a way to pattern match them and hide at the very least the password, but probably the username as well. So something like this would rock:

@sensitive_uri
REDIS=redis://user:pass@host/db

Which would result in

>>> import settings
>>> print(settings.REDIS)
redis://***:***@host/db

I think there would be value in just being able to pass a regex as well where all groups would be starred out, but I can't come up with an example right now.