Gather email addresses for a library's registry point of contact and DMCA point of contact

[leonardr]

To participate in the SimplyE ecosystem a library needs to provide three email addresses:

• A patron support address where patrons of that library can get help. This is currently sent in the Authentication For OPDS document as a mailto: URL in a link with rel="support".
• An email address for the library's DMCA Designated Agent. This should be sent in the Authentication For OPDS document as a mailto: URL in a link with rel="https://librarysimplified.org/rel/designated-agent/copyright" or something.
• A SimplyE support address so we can contact libraries whose circulation managers or library registrations have problems. Ideally this address would only be shared with the library registry.

The first step is to gather the two email addresses we don't currently gather. These are per-library settings, just like the patron support addresses.

[leonardr]

All these issues are related:

#913
#914
#915
https://github.com/NYPL-Simplified/library_registry/issues/55