Logs query direction <-> sort order sync: add data source support and document how to use it

**Why is this needed**: In https://github.com/grafana/grafana/pull/98722 support was implemented to sync the log ordering toggle in the Explore view with the Loki query direction. However, this functionality appears to be implicit or hardcoded for Loki, as I cannot replicate this behavior for a custom, non-Loki data source. This leads to a disjointed UX where the data source returns logs in a specific order, but the Explore UI sort toggle does not reflect that state. **What would you like to be added**: I would like documentation added to https://grafana.com/developers/plugin-tools/tutorials/build-a-logs-data-source-plugin explaining how a custom data source can signal the log sort order to the Explore view.Specifically, how to populate the DataFrame or Metadata so that the "Oldest First / Newest First" UI toggle reflects the actual order of the returned data. I am primarily looking for one-way sync (Data Source $\to$ Explore UI), though bi-directional sync (Explore UI $\to$ Data Source query) would be ideal. **Who is this feature for?** Most logs users