t2165: add manifest for PersonasUI OMS (reference) App

This is a stand-alone manifest that defines the bare-minimum for
the OMS Personas UI reference App. This is intended to be used
with a CoreID Registry.

By default, the admin UI and default admin user are disabled in
the manifest, but can easily be enabled and updated if needed.

Set the URL to the CoreID Registry API in constance, along with
the App's scope and client for OIDC, and OIDC's base URL.

Ensure the django admin UI URLs, admin user fixture, and CoreID
test fixture are all within reach, disabled by default but
included in the manifest.
t1211: Fix PortalRegistry.yaml manifest for v0.8.5