type==logs also for hidden data streams

[ruflin]

Some time ago we added support for hidden data streams to the package spec. Endpoint is using this feature here. Another discussion around hidden data streams for the migration assistant is happening in elastic/elasticsearch#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.