Add a RAC-specific schema

[a-berish]

Is your feature request related to a problem? Please describe.
The DACS single-level required schema will fail for RAC resources because we do not have rights statements documented within archivesspace resource records, so the metadata rights declarations field in the resource JSON will always be blank.

Describe the solution you'd like
Add a RAC-specific schema that uses all of the DACS single-level required elements except for Rights Statements for Archival Description (metadata rights declarations)

Additional context
We should consider adding other local RAC-required notes:

• Administrative/Biographical History Element
• Arrangement
• Conditions Governing Use
• Immediate Source of Acquisition