Reference to local OEM non-JSON schema location

The JsonSchema resource is just to point to JSON Schema files; it's not meant to be used for CSDL or OpenAPI.

The text you have highlighted from the $metadata definition is a bit incorrect. The first bullet should be "an absolute URI"; it does not need to be a standard URI. Essentially it either needs to point to some web server hosting the schema file (which could be the DMTF site, a vendor website, or some private website in the infrastructure), or to a local copy of the XML file on the manager.

For OpenAPI, the same rules apply; we define a standard location for the OpenAPI document to be /redfish/v1/openapi.yaml, and its up to the contents of the file to describe where to go next, which would either be absolute URIs to other schema files, or relative URIs to local copies on the manager.