[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.

Written by the indexing model from the issue text.