Tighten EDOT reference page openings and contextualize flagged H1s

[Copilot]

This updates the five EDOT reference pages flagged by the page-openings sweep so their titles and introductions identify the page scope immediately. The edits make the openings more specific, product-aware, and easier to scan without changing page structure or technical guidance.

• Contextualize page titles

  • Renames the mOTLP rate limiting H1 to Managed OTLP Endpoint rate limiting.
  • Renames the hosts/VMs architecture H1 to explicitly identify it as EDOT architecture guidance.

• Strengthen page openings

  • Rewrites the opening paragraphs for:
    • architecture/hosts_vms.md
    • compatibility/limitations.md
    • compatibility/nomenclature.md
    • data-streams.md
    • motlp/rate-limiting.md
  • Moves the page purpose into the first one to two sentences and adds the missing product/feature context where needed.

• Keep changes surgical

  • Limits the update to H1s and introductory copy on the flagged pages.
  • Leaves the underlying guidance, structure, and downstream content unchanged.

Example of the style change applied:

# Managed OTLP Endpoint rate limiting [motlp-rate-limiting]

The Elastic Cloud Managed OTLP Endpoint (mOTLP) rate limits requests when your telemetry arrives faster than Elastic can process and index it into Elasticsearch. This page explains how rate limiting works, how to identify HTTP `429` responses, and what to do for Elastic Cloud Hosted and Serverless deployments.