[Doc] Expand documentation for data streams

[karenzone]

Related: elastic/logstash#12178
Suggested as follow-up to: #988

Enhancements for consideration:

• Expand descriptions/plugin behavior for time series and non-time series data
  • Do we need to explain difference in indexing strategy?
• Include examples for basic default config, custom data stream name. (Doc: Add data stream section and config samples #1009)
• Expand ECS section to list of ES-compatible plugins and caveat against introducing fields that conflict with ECS
• Explain special treatment for data coming from Elastic Agent

While we're making doc changes, perhaps we can resolve items in #978 at the same time.

[karenzone]

cc:/ @kares