fix(server): always enable Kura cross-region replication

What changed

• Removes TUIST_KURA_CROSS_REGION_REPLICATION_ENABLED.
• Always configures managed Kura regions with the shared cross-region peer TLS secret.
• Pins the managed-region configuration in Tuist.Kura.RegionsTest.

Why

The flag was not a useful safe rollout lever anymore. It only gated peerTLSSecretName, while the 0.8.0 server still emits the new cross-region CRD fields such as peerPublicHost and globalDiscoveryDNSName. That means disabling the flag does not make old regional CRDs/controllers compatible with new server manifests.

Cross-region replication is now the intended behavior for managed Kura regions, so the control-plane configuration should be unconditional and regional clusters should be upgraded in lockstep with the 0.8.0 CRD/controller/runtime.

Rollout notes

Regional clusters still need the 0.8.0 CRDs and Kura controller before new regional KuraInstances can be created. This PR removes the misleading partial opt-out instead of preserving a flag that cannot actually protect old regional controllers.

Validation

• mix format lib/tuist/environment.ex lib/tuist/kura/regions.ex test/tuist/environment_test.exs test/tuist/kura/regions_test.exs
• mix test test/tuist/kura/regions_test.exs compiled the app, then failed while preparing the local test database because the local DB schema is not set up: ERROR 42P01 (undefined_table) relation "users" does not exist.