Add cron jobs (#60)

* feat: finish up cron jobs

* feat: clean up

api/backend/database/schema/schema.py

@@ -17,4 +17,14 @@ CREATE TABLE IF NOT EXISTS users (
     full_name STRING,
     disabled BOOLEAN
 );
+
+CREATE TABLE IF NOT EXISTS cron_jobs (
+    id STRING PRIMARY KEY NOT NULL,
+    user_email STRING NOT NULL,
+    job_id STRING NOT NULL,
+    cron_expression STRING NOT NULL,
+    time_created DATETIME NOT NULL,
+    time_updated DATETIME NOT NULL,
+    FOREIGN KEY (job_id) REFERENCES jobs(id)
+);
 """