feat: keep the materials index in sync and add bm:materials-reindex

- the materials admin syncs after create and update and removes after
  delete, once the save transaction commits (UseMaterialIndex, set at Boot)
- POST and PUT /api/v1/bm/materials sync after the transaction, DELETE
  removes the document (its statement has no primary key, so no callback)
- bm:materials-reindex [--fresh] [--if-configured] ensures the index and
  syncs every material; it refuses without an engine and runs nightly
  at 04:15 with --if-configured
- TestMaterialSearchAgainstDatabase (Postgres) is written for the final
  verification phase

postgres_test.go

@@ -136,13 +136,19 @@ func testDatabase(t *testing.T) (*sql.DB, string) {
 // migrated activates golem15.user and jz.bm, migrates a fresh database and
 // publishes it on the application, as serve does.
 func migrated(t *testing.T) (*backpack.App, []party.Plugin, *gorm.DB) {
+	t.Helper()
+	return migratedWith(t)
+}
+
+// migratedWith is migrated with env added to the application config.
+func migratedWith(t *testing.T, env ...string) (*backpack.App, []party.Plugin, *gorm.DB) {
 	t.Helper()
 	sqlDB, _ := testDatabase(t)
 	gdb, err := lagoon.Use(t.Context(), sqlDB)
 	if err != nil {
 		t.Fatalf("lagoon.Use: %v", err)
 	}
-	app := backpack.New(testConfig(t))
+	app := backpack.New(testConfig(t, env...))
 	plugins := activate(t, app)
 	if err := lagoon.Migrate(gdb, plugins); err != nil {
 		t.Fatalf("lagoon.Migrate: %v", err)