Added created_at & updated_at columns to key_value (#433)

ref https://linear.app/ghost/issue/AP-871

Added timestamps to our entries in the key_value table is going to help us
understand exactly _when_ we recieve an incoming activity. This can go a long
way in allowing us to correlate data and investigate bugs.

Author: allouis

migrate/migrations/000027_add-created-at-to-key-value-table.down.sql

@@ -0,0 +1,3 @@
+ALTER TABLE `key_value`
+DROP COLUMN `created_at`,
+DROP COLUMN `updated_at`;

migrate/migrations/000027_add-created-at-to-key-value-table.up.sql

@@ -0,0 +1,3 @@
+ALTER TABLE `key_value`
+ADD COLUMN `created_at` TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP,
+ADD COLUMN `updated_at` TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP;