add cron job to clean duckdb index cache
We have a cache folder in `/storage/duckdb-index`, this folder is used for cached downloads in `/search` and `/filter` while calling `  hf_hub_download` https://github.com/huggingface/datasets-server/blob/ef8a1cb34ba661b859962ac8d6c138374a0b0190/libs/libapi/src/libapi/duckdb.py#L78 (which needs a cache directory).
I noticed that we have old files in `/storage/duckdb-index/cache` which are using about 185G:
![image](https://github.com/huggingface/datasets-server/assets/5564745/3af4c5b6-eb5e-4bbb-9df3-5672dbc84173)

We can apply the same cleaning as we do for other folders so I added a new cron job.
I think another approach to avoid using `hf_hub_download` cache is to use `hf_transfer` directly, but I will investigate more about the advantages, meanwhile, the cron job will avoid increasing the storage usage.

add cron job to clean duckdb index cache: We have a cache folder in `/storage/duckdb-index`, this folder is used for cached downloads in `/search` and `/filter` while calling `  hf_hub_download` https://github.com/huggingface/datasets-server/blob/ef8a1cb34ba661b859962ac8d6c138374a0b0190/libs/libapi/src/libapi/duckdb.py#L78 (which needs a cache directory).
I noticed that we have old files in `/storage/duckdb-index/cache` which are using about 185G:
![image](https://github.com/huggingface/datasets-server/assets/5564745/3af4c5b6-eb5e-4bbb-9df3-5672dbc84173)

We can apply the same cleaning as we do for other folders so I added a new cron job.
I think another approach to avoid using `hf_hub_download` cache is to use `hf_transfer` directly, but I will investigate more about the advantages, meanwhile, the cron job will avoid increasing the storage usage.
