feat(backend) move module scheduler

backend/server/src/scheduler/tasks/mod.rs

@@ -0,0 +1,8 @@
+use chrono::{DateTime, Utc};
+
+pub mod basic;
+
+pub trait Task: Send + Sync {
+    fn get_next_execution(&self) -> Option<DateTime<Utc>>;
+    fn call(&self);
+}