Creating users via `hyrax/seed/setup.json` currently requires putting
hardcoded credentials into `setup.json`. Since this is a potential
security issue, we have decided to remove the support for setting
passwords at all through this file. Since `User` objects don't support a
`nil` password, we will now simply generate a random 32 byte / 256 bit
"password" (which may contain non-printable characters).

These passwords are not meant to be used/entered anyway, since login for
all users (including admins) is supposed to use either Shibboleth or
ORCID. However, since RDMS/Hyrax requires at least one admin user to
exist at the first startup in order to create the `CRC_1280_COLLECTION`
and the corresponding `crc_1280_manager` and `crc_1280_member` roles,
this commit also adds support for pre-seeding Shibboleth accounts via
`hyrax/seed/setup.json`.

Note that these users are primarily identified through their `uid`
attribute, which contains their Pairwise ID obtained from the Shibboleth
IDP, and *not* their email address. In fact, if the user's name or email
address changes on the IDP, the corresponding values in RDMS's user
database will be updated/replaced automatically with the new values
obtained from the IDP.