tsk-20: Add event to scheduled message (#23)

Closes #20

Reviewed-on: phoenix/textsender-api#23
Co-authored-by: phoenix <kundeng00@pm.me>
Co-committed-by: phoenix <kundeng00@pm.me>

migrations/schema.sql

@@ -21,3 +21,11 @@ CREATE TABLE scheduled_messages (
     status TEXT CHECK (status IN ('PENDING', 'READY', 'PROCESSING', 'DONE')),
     user_id UUID NOT NULL
 );
+
+CREATE TABLE scheduled_message_events (
+    id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
+    recipient_id UUID NOT NULL,
+    message_id UUID NOT NULL,
+    scheduled_message_id UUID NOT NULL,
+    created timestamptz DEFAULT now()
+)