Cells: Iteration 1: Make `GCK/GDK` to configure `cluster_main` connection

Read: &9667 (closed)

Change

Ensure that GCK/GDK can be configured in a Cells architecture by enabling cluster_main connection in config/database.yml.

• GDK
• GCK

Outcome

Once configured the GCK/GDK when running as Cell 2 could read/write application_settings from another database.