feat(auth): add scope documentation

[aldbr]

Add documentation about the scope following #300

The same string is repeated at 3 different locations in the code. While it is cumbersome (developers would need to update every instances of the doc to avoid any discrepancy, which will likely happen at some point), I don't see any other way of doing that as openapi reads the static documentation and I find it convenient to have the details when using the CLI or the openapi document.

Any opinion?

[chaen]

I think it is fine as it is. If really it is too much of an issue, you can put this in a constant, and set the __docs__ of a function to that constant. But I really don't think it's needed