Use features in search
The search endpoint was using the feature types from the arrow table returned by duckdb, which doesn't contain any metadata about the Image type.

So I added a `features` field to the `split-duckdb-index` job to store the feature types that the search endpoint can use to correctly load the image data.

I added a migration job to fill this field with `None` and I will simply update the `split-duckdb-index` job for image datasets.

Fix https://github.com/huggingface/datasets-server/issues/1713
Use features in search: The search endpoint was using the feature types from the arrow table returned by duckdb, which doesn't contain any metadata about the Image type.

So I added a `features` field to the `split-duckdb-index` job to store the feature types that the search endpoint can use to correctly load the image data.

I added a migration job to fill this field with `None` and I will simply update the `split-duckdb-index` job for image datasets.

Fix https://github.com/huggingface/datasets-server/issues/1713