Possible bug with overriding default admin key

[dzikowski]

Default admin public key is provided in DEV_ADMIN_PUBLIC_KEY env. It should be possible to change it with UpdatePublicKey method. We got some reports that it might not be working as expected. We need to verify if it is not possible to use the key from env once it is changed by UpdatePublicKey.

This issue deserves a thorough unit testing of this feature in PublicKeyContract.spec.ts