Add a dedicated :registration named logger that lets operators enable debug-level registration logging without flooding the main log with SQL queries or view rendering.

At the default info level, only session markers appear:
- session_start (GET /register) with org, location, hostgroup
- session_complete (POST /register) with host name, action (created/updated), duration_ms

At debug level, companion Katello PRs emit Candlepin per-call timing and cache HIT/MISS decisions using the same logger.

The logger is configured independently via settings.yaml:

:logging:
  :loggers:
    :registration:
      :level: debug