Provide registry support address to library registry upon registration

[leonardr]

The library registry can grab a library's patron support email and DMCA Designated Agent email from the library's public Authentication For OPDS document. But the point of contact for problems with the SimplyE ecosystem itself doesn't need to be public. This person is probably some random library or contractor employee and the only party that needs to know their email address is the library registry itself.

Upon registration, the library should provide this information either directly to the library registry, or by encrypting it with its temporary secret key and sticking the encrypted value in the temporary A4OPDS document retrieved by the registry.

[aslagle]

For the private email address, the library registry should create a public key and stick it in its main catalog document along with its register URL. The circ manager should retrieve that public key and use it to encrypt the email address, then either put the encrypted email in the register request or temporarily put it in the auth document. This is better than using the secret key generated on registration because the registry can return an error if the email is missing, rather than having to do a separate step after the library is already registered.