Many datasets have dots in their config names. However it causes issues with the YAML tags of the dataset cards since we can't have dots in YAML keys. 

I fix this, I removed the tags separations per config name completely, and have a single flat YAML for all configurations. Dataset search doesn't use this info anyway. I removed all the config names used as YAML keys, and I moved them in under a new `config:` key.

This is related to https://github.com/huggingface/datasets/pull/2362 (internal https://github.com/huggingface/moon-landing/issues/946).

Also removing the dots in the YAML keys would allow us to do as in https://github.com/huggingface/datasets/pull/4302 which removes a hack that replaces all the dots by underscores in the YAML tags.

I also added a test in the CI that checks that all the YAML tags to make sure that:

- they can be parsed using a YAML parser
- they contain only valid YAML tags like languages or task_ids
Remove config names as yaml keys
I included the change from https://github.com/huggingface/datasets/pull/4302 directly in this PR, this way the datasets will be updated right away in the CI (the CI is only triggered when a dataset card is changed) _The documentation is not available anymore as the PR was closed or merged._ Alright it's ready now :)

Here is an example for the `ade_corpus_v2` dataset card. Notice the new `configs` key:

https://github.com/huggingface/datasets/blob/76d9a141740a03f6836feb251f6059894b8d8046/datasets/ade_corpus_v2/README.md#L1-L78

CI failures are only related to dataset cards missing some content.