Refactor ApplicationConfig into a separate Custom Resource with its own controller

Summary

The current all-in-one GitLab CR is hard to manage and runs into technical limitations.

To decompose the CR, we need to decompose the ApplicationConfig first, because it's a dependency for ApplicationServer and JobProcessor.

Success criteria

• ApplicationConfig CR and controller created
• Controller reconciles a rails config
• Reference to the rails config is available in the CR status