config: repair installer for 17.1-BETA
config: repair installer for 17.1-BETA

The installer user is injected for install media login, but
we authenticate against our database now instead.  This has
larger consequences that require a persistent installer user,
which is not so easy to disable/defang after installation.

Hopefully this is temporary.

opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core