nextjs: Inject moduleMetadata on Turbopack builds

`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.