[wip] Add Elastic Distributions for OpenTelemetry docs

[colleenmcginnis]

Adds docs for Elastic Distributions for OpenTelemetry. Distro docs will be at elastic.co/guide/en/apm/open-telemetry/{language}.

Add new books to the config

• Java
  • Add to this repo 27f46ca
  • Merge docs in content repo [docs] Prepare docs  elastic-otel-java#328
• .NET
  • Add to this repo da93c02
  • Merge docs in content repo [docs] Prepare docs elastic-otel-dotnet#127
• Node.js
  • Add to this repo b41b176
  • Merge docs in content repo [docs] Prepare docs  elastic-otel-node#287

Other languages will be added in follow up PR(s).

Update navigation

• Update APM landing page (extra/apm_docs_landing.html)
• Add links to APM breadcrumb dropdown (resources/asciidoctor/lib/chunker/obs_breadcrumbs.rb)

Add shared attributes

TBD

cc @bmorelli25

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[colleenmcginnis]

We will not be publishing distro docs to elastic.co/guide. Instead, users will view docs as Markdown files in GitHub.