[refactor]: Remove isSSOEnabled logic throughout the codebase (#9462)

Eliminated all references to `isSSOEnabled` across the frontend,
backend, and configuration files. This change simplifies the codebase by
removing unnecessary feature flag checks, associated logic, and
environment variables. The SSO feature remains available without
reliance on this flag.

packages/twenty-server/src/database/typeorm-seeds/core/feature-flags.ts

@@ -50,11 +50,6 @@ export const seedFeatureFlags = async (
         workspaceId: workspaceId,
         value: true,
       },
-      {
-        key: FeatureFlagKey.IsSSOEnabled,
-        workspaceId: workspaceId,
-        value: true,
-      },
       {
         key: FeatureFlagKey.IsGmailSendEmailScopeEnabled,
         workspaceId: workspaceId,