Add proper decorator for interface holding non-resource operations

For the operations in the file `routes.tsp`, they are all non-resource operations. So the interface shouldn't be decorated by `@armResourceOperations`. If we don't decorate it with `@armResourceOperations`, the linter `@azure-tools/typespec-azure-resource-manager/arm-resource-interface-requires-decorator` violates.

We need a proper decorator and modify the message for `@azure-tools/typespec-azure-resource-manager/arm-resource-interface-requires-decorator`

Start by reading routes.tsp and the implementation of @azure-tools/typespec-azure-resource-manager/arm-resource-interface-requires-decorator, then run the linter against the interface. Done means non-resource operations have an appropriate decorator and the diagnostic message no longer incorrectly requires @armResourceOperations.

Written by the indexing model from the issue text.