Signature
Description
Stages a proposed new admin forpolicyId. The active admin does not change
until pendingAdmin calls finalizeUpdateAdmin.
Dev: Reverts with PolicyNotFound when policyId does not exist.
Dev: Reverts with Unauthorized when the caller is not the current admin.
Param: policyId Policy whose admin is being staged.
Param: newAdmin Proposed new admin, or address(0) to clear any pending nomination.