feat: add Discord OAuth integration and connector routes

- Introduced Discord OAuth support with new environment variables for client ID, client secret, and redirect URI.
- Implemented Discord connector routes for OAuth flow, including authorization and callback handling.
- Enhanced Discord connector to support both OAuth-based authentication and legacy bot token usage.
- Updated Discord indexing logic to utilize OAuth credentials with auto-refresh capabilities.
- Removed outdated Discord UI components and adjusted frontend logic to reflect the new integration.

surfsense_backend/app/routes/__init__.py

@@ -27,6 +27,7 @@ from .rbac_routes import router as rbac_router
 from .search_source_connectors_routes import router as search_source_connectors_router
 from .search_spaces_routes import router as search_spaces_router
 from .slack_add_connector_route import router as slack_add_connector_router
+from .discord_add_connector_route import router as discord_add_connector_router
 
 router = APIRouter()
 
@@ -46,6 +47,7 @@ router.include_router(linear_add_connector_router)
 router.include_router(luma_add_connector_router)
 router.include_router(notion_add_connector_router)
 router.include_router(slack_add_connector_router)
+router.include_router(discord_add_connector_router)
 router.include_router(new_llm_config_router)  # LLM configs with prompt configuration
 router.include_router(logs_router)
 router.include_router(circleback_webhook_router)  # Circleback meeting webhooks