[Account Settings] Allow admin to disable the curve grades feature in Gradebook

[hmcneill]

Problem statement:

When the curve grades option is used in gradebook it cannot be undone. This creates a risk if it is used in error, without understanding of the implications, or against institutional policy. https://community.canvaslms.com/t5/Canvas-Resource-Documents/Curving-Grades-in-Canvas/ta-p/387085

Proposed solution:

Add a sub-account setting option which would allow admin to disable the curve grades option and prevent it being used. This removes the risk and gives us control. Alternatively, the option could be controlled by adding a new granular permission, so access can be allowed for specific roles.

User role(s):

admin,instructor