Add application configuration for Sec DB

Proposal

We need to add support to the rails application for connecting to a separate Sec DB. This mirrors the CI implementation in intent and will unlock our ability to begin decomposition efforts per table and sectionsec domain

Implementation

• Introduce sec_decomposition_write feature flag
• Introduce sec_decomposition_read feature flag
• Introduce new ApplicationRecord class which connects to sec DB reliant on feature flags
• Update all relevant tables Phase 1 tables to inherit from new AR class (moved to individual table decomposition issues