Edit and restructure time series docs

[marciw]

(Replaces #3222, which was an ominshambles)

This PR restructures and edits time series data stream docs as part of #1502.

❗ Notes for reviewers:

• Changes were approved by Product and Engineering in Edit time series docs for clarity #3222 🙈
• The content is "MVP" quality overall. More improvements coming soon via the follow-up issue, including reconciling the time series section with recent similar changes to the general data stream docs
• The various applies_to thingies could probably be better; I am committed to maintaining the thinnest of grasps on applies_to metadata

Summary of changes:

• Accuracy updates by SME reviewers/contributors
• Many edits for clarity, conciseness, and user focus
• Mentions of new ES|QL TS command (which was one of the primary motivators for cleaning up this section)
• See also Consolidate time series downsampling docs #2274 and Add time series data stream quickstart #2742

[github-actions]

🔍 Preview links for changed docs

• manage-data/data-store/data-streams/advanced-topics-tsds.md
• manage-data/data-store/data-streams/time-bound-tsds.md
• manage-data/data-store/data-streams/tsds-ingest-otlp.md
• manage-data/data-store/data-streams/downsampling-time-series-data-stream.md
• manage-data/data-store/data-streams/query-downsampled-data.md
• manage-data/data-store/data-streams/quickstart-tsds.md
• manage-data/data-store/data-streams/reindex-tsds.md
• manage-data/data-store/data-streams/run-downsampling.md
• manage-data/data-store/data-streams/set-up-tsds.md
• manage-data/data-store/data-streams/time-series-data-stream-tsds.md

[marciw]

Note for reviewers: The OTLP page was added in #3360 (written by @felixbarny)

Slated for more improvements in #3179

[marciw]

Note for reviewers: This is a new page, but the content isn't new. It used to be part of the main/overview page. We decided to split off the content because it's sort of advanced/extra.

Includes a round of techwriterly edits