Config-level dataset info
Will solve https://github.com/huggingface/datasets-server/issues/864

Part of https://github.com/huggingface/datasets-server/issues/735

I preserved the old name (without leading "/") for dataset-level step - `"dataset-info"` and named config-level step `"config-info"` because  `"dataset-dataset-info"` and  `"config-dataset-info"` look a bit silly to me but I don't have a strong opinion here, let me know what you think.

`config-info` result format is dict with info, `dataset-info` result format remained the same (dict[config_name, infos]), like this:
* `config-info`
```
dataset_info: {
    "description": "_DESCRIPTION",
    "citation": "_CITATION",
    "homepage": "_HOMEPAGE",
    ...
}
```
* `dataset-info`
```
dataset_info: {
"config_1": {
    "description": "_DESCRIPTION",
    "citation": "_CITATION",
    "homepage": "_HOMEPAGE",
    ...
  },
"config_2": {
    "description": "_DESCRIPTION",
    "citation": "_CITATION",
    "homepage": "_HOMEPAGE",
    ...
  },
}
```

I'm not sure why CI is broken.
Config-level dataset info: Will solve https://github.com/huggingface/datasets-server/issues/864

Part of https://github.com/huggingface/datasets-server/issues/735

I preserved the old name (without leading "/") for dataset-level step - `"dataset-info"` and named config-level step `"config-info"` because  `"dataset-dataset-info"` and  `"config-dataset-info"` look a bit silly to me but I don't have a strong opinion here, let me know what you think.

`config-info` result format is dict with info, `dataset-info` result format remained the same (dict[config_name, infos]), like this:
* `config-info`
```
dataset_info: {
    "description": "_DESCRIPTION",
    "citation": "_CITATION",
    "homepage": "_HOMEPAGE",
    ...
}
```
* `dataset-info`
```
dataset_info: {
"config_1": {
    "description": "_DESCRIPTION",
    "citation": "_CITATION",
    "homepage": "_HOMEPAGE",
    ...
  },
"config_2": {
    "description": "_DESCRIPTION",
    "citation": "_CITATION",
    "homepage": "_HOMEPAGE",
    ...
  },
}
```

I'm not sure why CI is broken.