Code refactoring and feature implementation

[lahirujayathilake]

Changes

• Refactored service-to-service communication: Moved to dependency-based interactions.
• Upgraded Keycloak to version 20: Improved security and features.
• Implemented OIDC standards: Aligned authorization, token, and OIDC endpoints. (changes to the params and responses)
• Removed Nginx reverse proxy
• Introduced PKCE flow: Suitable for Single Page Applications
• Introduced JWKS endpoint: Enabled public key verification.
• Customized token generation: Injected groups and scopes for fine-grained authorization.

Module Architecture

• custos-application: Entry point, configuration, and API integration.
• custos-core: Core business logic, entities, and repositories.
• custos-services: Service classes for business logic implementation.
• custos-api: REST controllers for exposing application functionality.