[DOCS]: Document Backend Refactoring and New Architecture

[Abradat]

Documentation Topic

Document the refactored backend code and explain the new code and deployment architecture.

Description

• Document the refactored backend code that can use Postgres and Oracle as the primary database.
• Document the new architecture for Silva deployments in dev and test environments.

Related Files or URLs

No response

Additional Notes

No response

[Abradat]

• Add Oracle to PostgreSQL: Backend Refactor Confluence documentation.
• Update Oracle to PostgreSQL: Migration History Confluence document with recent changes.
• Add backend Readme.md file for running backend with different database docs(#1163): add backend README with setup instructions #1179

[Abradat]

Add: Oracle to PostgreSQL: Deployment Architecture (Dual Primary DB: Oracle + PostgreSQL)