Enable LogsDB by default for `logs-*-*` for stateful deployments

[salvatore-campagna]

Description

We will introduce the new index.mode "logs" as a tech preview in Elasticsearch 8.15. As a result, while in tech preview, the choice of adopting the new index mode is up to integrations.

After we decide which Elasticsearch version will introduce LogsDB as Generally Available the new index mode we need, anyway, to apply the new index mode "logs" by default to all logs-*-* index templates.

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)

[ruflin]

the choice of adopting the new index mode is up to integrations.

As long as the logsdb mode is in tech preview, I don't think integrations can adopt it especially as long as not all fields are supported because otherwise it could be a breaking change for our users. What we can do is start testing / benchmarking with logsdb.