chore: incoming webhooks description migration (#5803)

https://linear.app/unleash/issue/2-1822/incoming-webhooks-add-description

A description field will help us better distinguish incoming webhooks
and their purpose.

src/migrations/20240109093021-incoming-webhooks-description.js

@@ -0,0 +1,12 @@
+exports.up = function (db, cb) {
+    db.runSql(
+        `
+        ALTER TABLE incoming_webhooks ADD COLUMN IF NOT EXISTS description TEXT;
+        `,
+        cb,
+    );
+};
+
+exports.down = function (db, callback) {
+    callback();
+};