Additional improvements to time series data stream docs

[marciw]

Some of these can be 9.2 "fast-follow" improvements, others are just "later" for no particular deadline. Not yet prioritized

specific:

• OTLP: edit more thoroughly
• Reindex: explain op_type (add something like "ensures the operation is idempotent")
• Reindex: update to "better path" mentioned here

general:

• More glue (and consistency) with general data streams docs
• Other cross-linking opportunities
• More ES|QL TS command coverage (examples etc.)
• Any additional advanced operations