Add/align 'Data streams' content

[kilfoyle]

This adds Manage data / The Elasticsearch data store / Data streams as well as a "Manage data streams" page that has the UI steps.

I've also removed the "logsdb.md" and "tsdb.md" pages (in red) since they are duplicates of the "Logs data stream" and "Time series data stream (TSDS)" pages (in green):

NOTE: As proposed here, after this is merged I'd like to bump the "Data streams" section one level higher, rather than have it nested under "index types".

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Previews:

• Data streams
• Manage a data stream

Closes: https://github.com/elastic/docs-projects/issues/379

[kilfoyle]

I'm going to revise this to move the Data Streams content up one level, as I proposed here.

[colleenmcginnis]

This approach makes sense to me! And thanks for cleaning up those duplicate pages. ✨