nextjs: Inject moduleMetadata on Turbopack builds #23402

moduleMetadata only reaches the webpack plugin. On Turbopack builds it has no effect — #23372 added a build-time warning and documented it as webpack-only rather than leaving it a silent no-op.

The Turbopack loader (moduleMetadataInjectionLoader) already does the injection, but hardcodes the applicationKey payload. To close the gap: merge arbitrary metadata alongside the applicationKey tag, resolve the ModuleMetadataCallback form (releaseName is already resolved in getFinalConfigObject.ts and needs threading through), and widen the loader gate to applicationKey || moduleMetadata. Then drop the warning and the JSDoc note.

Touches the default bundler path for Next.js 16+, so it wants e2e coverage.