feat: add created_at/updated_at columns to cluster and machines store tables

internal/machine/store/schema.sql

@@ -1,31 +1,36 @@
 -- cluster table stores the key-value pairs of the cluster configuration.
 CREATE TABLE cluster
 (
-    key   TEXT NOT NULL PRIMARY KEY,
-    value ANY
+    key        TEXT      NOT NULL PRIMARY KEY,
+    value      ANY,
+    -- updated_at is the last time the value was written.
+    updated_at TIMESTAMP NOT NULL DEFAULT '1970-01-01 00:00:00'
 );
 
 -- machines table stores the basic information of the machines in the cluster.
 CREATE TABLE machines
 (
-    id   TEXT NOT NULL PRIMARY KEY,
-    name TEXT AS (json_extract(info, '$.name')),
+    id         TEXT      NOT NULL PRIMARY KEY,
+    name       TEXT AS (json_extract(info, '$.name')),
     -- info is a JSON-serialized MachineInfo protobuf message.
-    info TEXT NOT NULL DEFAULT '{}' CHECK (json_valid(info))
-    -- TODO: add created_at and updated_at fields to track machine age and last update time.
+    info       TEXT      NOT NULL DEFAULT '{}' CHECK (json_valid(info)),
+    -- created_at is the time the machine record was created.
+    created_at TIMESTAMP NOT NULL DEFAULT '1970-01-01 00:00:00',
+    -- updated_at is the last time the machine record was updated.
+    updated_at TIMESTAMP NOT NULL DEFAULT '1970-01-01 00:00:00'
 );
 
 -- containers table stores the Uncloud-managed Docker containers created in the cluster.
 CREATE TABLE containers
 (
-    id           TEXT NOT NULL PRIMARY KEY,
+    id           TEXT      NOT NULL PRIMARY KEY,
     -- container is a JSON-serialized api.ServiceContainer struct.
-    container    TEXT NOT NULL DEFAULT '{}' CHECK (json_valid(container)),
-    machine_id   TEXT NOT NULL DEFAULT '',
+    container    TEXT      NOT NULL DEFAULT '{}' CHECK (json_valid(container)),
+    machine_id   TEXT      NOT NULL DEFAULT '',
     service_id   TEXT AS (json_extract(container, '$.Config.Labels."uncloud.service.id"')),
     service_name TEXT AS (json_extract(container, '$.Config.Labels."uncloud.service.name"')),
     -- sync_status indicates if the record reflects the actual Docker state of the container.
-    sync_status  TEXT NOT NULL DEFAULT '',
+    sync_status  TEXT      NOT NULL DEFAULT '',
     -- updated_at is the last time the record was updated.
     updated_at   TIMESTAMP NOT NULL DEFAULT '1970-01-01 00:00:00'
 );