Heading shortcode doesn't generate anchor IDs for Japanese localization

**This is a Bug Report**

**Problem:**
While translating the [Init containers page](https://kubernetes.io/docs/concepts/workloads/pods/init-containers/) into Japanese, I encountered an internal link that references the "What's next" section.

> This simple example should provide some inspiration for you to create your own init containers. [What's next](https://kubernetes.io/docs/concepts/workloads/pods/init-containers/#what-s-next) contains a link to a more detailed example.

However, the `heading` shortcode doesn't generate anchor IDs when used in Japanese documentation, breaking internal page links that reference those headings.

Currently, manually adding `{#what-s-next}` after the shortcode works as a workaround, but this was flagged as incorrect in [#53639](https://github.com/kubernetes/website/pull/53639#discussion_r2649674434).

**Proposed Solution:**
Include anchor IDs in the i18n translation strings in `i18n/ja/ja.toml`:

```toml
[whatsnext_heading]
other = "次の項目 {#what-s-next}"
```

I tested this locally and confirmed that anchor links work correctly with this approach. But is this the correct approach for handling anchor IDs in translations?

**Page to Update:**
- `i18n/ja/ja.toml` and any Japanese documentation pages using heading shortcodes with internal links