type==logs also for hidden data streams

Some time ago we added support for hidden data streams to the package spec. Endpoint is using this feature [here](https://github.com/elastic/package-storage/blob/production/packages/endpoint/0.18.0/data_stream/collection/manifest.yml#L4). Another discussion around hidden data streams for the migration assistant is happening in https://github.com/elastic/elasticsearch/pull/68737. One question this brought up, is if the type for hidden indices should be `.logs` or `logs`.

To not introduce any new types, it is preferable that even if the data stream starts with a `.`, the type is still `logs` and not `.logs`.

This issue is to discuss the above further and in case we agree with `logs` as type, follow up to make sure we update implementations if needed.