fix: [torrust#56} default user registration date with time

When we import users from previous versions where the app did not store
the registration date we assign the current datetime for the registration.

src/upgrades/from_v1_0_0_to_v2_0_0/upgrader.rs

@@ -16,7 +16,7 @@ use crate::config::Configuration;
 
 fn today_iso8601() -> String {
     let dt: DateTime<Utc> = SystemTime::now().into();
-    format!("{}", dt.format("%Y-%m-%d"))
+    format!("{}", dt.format("%Y-%m-%d %H:%M:%S"))
 }
 
 async fn current_db() -> Arc<SqliteDatabaseV1_0_0> {