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.
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