[i18n] Factor prose out of shortcodes like `docs/latest-release`

[chalin]

This idea is to separate concerns, and put prose in includes files and code in shortcodes.

Context:

• [ja] translate collector/distributions page #6337 and other non-en languages
• https://deploy-preview-6337--opentelemetry.netlify.app/ja/docs/collector/distributions/

Tasks

• [Collector] Slight rewording of distributions and release info #6476
• [infra] Factor out include partial from shortcode #6494
• [i18n] Convert docs/exporter shortcodes into includes #6581
• [i18n] Separate prose out of Convert docs/exporter/intro.md, and other improvements #6583
• Consider moving content/en/docs/_includes/exporters/intro.md to be under docs/languages/_includes, and using an absolution site-specific path in the shortcode.
• ...

Related:

• Eliminate no-duplicate-heading exception from pages like exporters