[Devcontainers frontend plugin] Make the component hidden if no annotation is present

If the annotation is not present, make the `DevcontainersProvider` component hidden.

This should be working in `packages/app/src/components/catalog/EntityPage.tsx`:

```









```

The `isDevContainersAvailavble` function should check if the correct annotations are in place like (pseudocode):
```
export const isDevContainersAvailable = (entity: Entity) =>
Boolean(entity.metadata.annotations?.[DEVCONTAINERS_ANNOTATION]);
```

This way the item can be hidden and the page can be cleaner.

Start in packages/app/src/components/catalog/EntityPage.tsx and inspect the DevcontainersProvider EntitySwitch case, along with the existing DEVCONTAINERS_ANNOTATION and isDevContainersAvailable references. Done means the component is hidden when the annotation is absent and remains visible when the correct annotation is present.

索引モデルが issue の本文から書いたものです。