feat: CREATE INDEX CONCURRENTLY for "userId" "id" composite note index if admin wish. (#15915)

* chore: CREATE INDEX CONCURRENTLY for "userId" "id" composite note index

* chore: remove { concurrent: true } and comment why

* update comment

* feat: add MISSKEY_MIGRATION_CREATE_INDEX_CONCURRENTLY option

* fix: spdx license header

* alter comment

* chore: improve behavior when migration failure

* docs(changelog): 2025.4.1 で追加されたインデックスの再生成をノートの追加しながら行えるようになりました

* ちょっと表現を変更

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Co-authored-by: 饺子w (Yumechi) <35571479+eternal-flame-ad@users.noreply.github.com>

packages/backend/ormconfig.js

@@ -1,6 +1,7 @@
 import { DataSource } from 'typeorm';
 import { loadConfig } from './built/config.js';
 import { entities } from './built/postgres.js';
+import { isConcurrentIndexMigrationEnabled } from "./migration/js/migration-config.js";
 
 const config = loadConfig();
 
@@ -14,4 +15,5 @@ export default new DataSource({
 	extra: config.db.extra,
 	entities: entities,
 	migrations: ['migration/*.js'],
+	migrationsTransactionMode: isConcurrentIndexMigrationEnabled() ? 'each' : 'all',
 });