feat(dcl): extend CreateConnectionCommand with backup config and failover retry count

Update CreateConnectionCommand to carry PrimaryConnectionDetails,
BackupConnectionDetails, and FailoverRetryCount. Update all callers:
DataConnectionManagerActor, DataConnectionActor, DeploymentManagerActor,
FlatteningService, and ConnectionConfig. The actor stores both configs
but continues using primary only — failover logic comes in Task 3.

src/ScadaLink.TemplateEngine/Flattening/FlatteningService.cs

@@ -90,7 +90,9 @@ public class FlatteningService
                         connections[attr.BoundDataConnectionName] = new ConnectionConfig
                         {
                             Protocol = conn.Protocol,
-                            ConfigurationJson = conn.PrimaryConfiguration
+                            ConfigurationJson = conn.PrimaryConfiguration,
+                            BackupConfigurationJson = conn.BackupConfiguration,
+                            FailoverRetryCount = conn.FailoverRetryCount
                         };
                     }
                 }