Use tenant agnostic role for providing `Microsoft.Insights/autoscalesettings/Write` permission

[tevoinea]

The Function App needs Microsoft.Insights/autoscalesettings/Write permissions from a built-in role so that it can be used across any azure tenant. The only role that meets this criteria is the Contributor role.

Docs: https://docs.microsoft.com/en-us/azure/role-based-access-control/built-in-roles#all