feat(agent): Add docker image update available flag (#2211)

Co-authored-by: henrygd <hank@henrygd.me>

internal/migrations/1789079746_container_update_available.go

@@ -0,0 +1,24 @@
+package migrations
+
+import (
+	"github.com/pocketbase/pocketbase/core"
+	m "github.com/pocketbase/pocketbase/migrations"
+)
+
+func init() {
+	m.Register(func(app core.App) error {
+		collection, err := app.FindCollectionByNameOrId("containers")
+		if err != nil {
+			return err
+		}
+		collection.Fields.Add(&core.BoolField{Name: "updatable"})
+		return app.Save(collection)
+	}, func(app core.App) error {
+		collection, err := app.FindCollectionByNameOrId("containers")
+		if err != nil {
+			return err
+		}
+		collection.Fields.RemoveByName("updatable")
+		return app.Save(collection)
+	})
+}