Basic stats
Started a `/basic-stats` endpoints that computes histogram for numerical data using dask.

Not sure if we want to merge this feature right away, I implemented this mostly to trigger some discussions on how to add new data aggregates: does this way sound correct to you ?

Feel free to also comment on how we could expand this to include stats for non-numerical columns. How can we add new stats that would be returned in the same endpoint ?

You can try it on `__DUMMY_DATASETS_SERVER_USER__/letters` for example:

<details>

<summary>Results of `/basic-stats` on `__DUMMY_DATASETS_SERVER_USER__/letters`</summary>

```json
{
    "basic_stats": [
        {
            "dataset": "__DUMMY_DATASETS_SERVER_USER__/letters",
            "config": "__DUMMY_DATASETS_SERVER_USER__--letters",
            "split": "train",
            "column_name": "label",
            "histogram": {
                "hist": [
                    10,
                    0,
                    0,
                    0,
                    0,
                    11,
                    0,
                    0,
                    0,
                    5
                ],
                "bin_edges": [
                    0.0,
                    0.2,
                    0.4,
                    0.6,
                    0.8,
                    1.0,
                    1.2,
                    1.4,
                    1.6,
                    1.8,
                    2.0
                ]
            }
        },
        {
            "dataset": "__DUMMY_DATASETS_SERVER_USER__/letters",
            "config": "__DUMMY_DATASETS_SERVER_USER__--letters",
            "split": "train",
            "column_name": "id",
            "histogram": {
                "hist": [
                    3,
                    2,
                    3,
                    2,
                    3,
                    2,
                    3,
                    2,
                    3,
                    3
                ],
                "bin_edges": [
                    0.0,
                    2.5,
                    5.0,
                    7.5,
                    10.0,
                    12.5,
                    15.0,
                    17.5,
                    20.0,
                    22.5,
                    25.0
                ]
            }
        },
        {
            "dataset": "__DUMMY_DATASETS_SERVER_USER__/letters",
            "config": "__DUMMY_DATASETS_SERVER_USER__--letters",
            "split": "train",
            "column_name": "fr_scrabble_value",
            "histogram": {
                "hist": [
                    10,
                    3,
                    3,
                    3,
                    0,
                    0,
                    0,
                    2,
                    0,
                    5
                ],
                "bin_edges": [
                    1.0,
                    1.9,
                    2.8,
                    3.7,
                    4.6,
                    5.5,
                    6.4,
                    7.3,
                    8.2,
                    9.1,
                    10.0
                ]
            }
        }
    ]
}
```

</details>

TODO:
- [ ] tests
- [ ] docs

cc @severo 

related to https://github.com/huggingface/datasets-server/issues/376
Basic stats: Started a `/basic-stats` endpoints that computes histogram for numerical data using dask.

Not sure if we want to merge this feature right away, I implemented this mostly to trigger some discussions on how to add new data aggregates: does this way sound correct to you ?

Feel free to also comment on how we could expand this to include stats for non-numerical columns. How can we add new stats that would be returned in the same endpoint ?

You can try it on `__DUMMY_DATASETS_SERVER_USER__/letters` for example:

<details>

<summary>Results of `/basic-stats` on `__DUMMY_DATASETS_SERVER_USER__/letters`</summary>

```json
{
    "basic_stats": [
        {
            "dataset": "__DUMMY_DATASETS_SERVER_USER__/letters",
            "config": "__DUMMY_DATASETS_SERVER_USER__--letters",
            "split": "train",
            "column_name": "label",
            "histogram": {
                "hist": [
                    10,
                    0,
                    0,
                    0,
                    0,
                    11,
                    0,
                    0,
                    0,
                    5
                ],
                "bin_edges": [
                    0.0,
                    0.2,
                    0.4,
                    0.6,
                    0.8,
                    1.0,
                    1.2,
                    1.4,
                    1.6,
                    1.8,
                    2.0
                ]
            }
        },
        {
            "dataset": "__DUMMY_DATASETS_SERVER_USER__/letters",
            "config": "__DUMMY_DATASETS_SERVER_USER__--letters",
            "split": "train",
            "column_name": "id",
            "histogram": {
                "hist": [
                    3,
                    2,
                    3,
                    2,
                    3,
                    2,
                    3,
                    2,
                    3,
                    3
                ],
                "bin_edges": [
                    0.0,
                    2.5,
                    5.0,
                    7.5,
                    10.0,
                    12.5,
                    15.0,
                    17.5,
                    20.0,
                    22.5,
                    25.0
                ]
            }
        },
        {
            "dataset": "__DUMMY_DATASETS_SERVER_USER__/letters",
            "config": "__DUMMY_DATASETS_SERVER_USER__--letters",
            "split": "train",
            "column_name": "fr_scrabble_value",
            "histogram": {
                "hist": [
                    10,
                    3,
                    3,
                    3,
                    0,
                    0,
                    0,
                    2,
                    0,
                    5
                ],
                "bin_edges": [
                    1.0,
                    1.9,
                    2.8,
                    3.7,
                    4.6,
                    5.5,
                    6.4,
                    7.3,
                    8.2,
                    9.1,
                    10.0
                ]
            }
        }
    ]
}
```

</details>

TODO:
- [ ] tests
- [ ] docs

cc @severo 

related to https://github.com/huggingface/datasets-server/issues/376