[i18n] Separate prose out of Convert docs/exporter/intro.md, and other improvements

[chalin]

• Followup to [i18n] Convert docs/exporter shortcodes into includes #6581
• Contributes to [i18n] Factor prose out of shortcodes like docs/latest-release #6460
• Refactors the layouts/shortcodes/docs/languages/exporters/intro.md shortcode, pulling out all the prose and putting it in an include file. We're still using the shortcode, because there's some logic in there used to initialize variables.
• Adds extra logic to the new shortcode so that we don't need to pass in the language ID anymore.

Previews

• https://deploy-preview-6583--opentelemetry.netlify.app/docs/languages/cpp/exporters/
• https://deploy-preview-6581--opentelemetry.netlify.app/docs/languages/go/exporters/
• https://deploy-preview-6581--opentelemetry.netlify.app/pt/docs/languages/python/exporters/

Diff

There is no significant change to the generated site files:

$ (cd public && git diff -I "dateModified|modified_time|data-proofer|^\s+[0-9a-f]+\.\.[0-9a-f]+</a>" -- ':(exclude)*.xml') | grep ^diff
diff --git a/site/index.html b/site/index.html

The last regex alternative of the argument to git diff -I is so that we ignore the "This page has drifted" callout's GitHub diff URL, which has changed.

[chalin]

The content of this file is essentially the prose that was in the old version of layouts/shortcodes/docs/languages/exporters/intro.md.

[tiffany76]

RSLGTM.

[theletterf]

LGMT.

Tangentially related question: Do we hash includes and track them for localization drift?

[chalin]

Tangentially related question: Do we hash includes and track them for localization drift?

Yes, given that the include pages are under content, they get checked by our i18n check script to ensure that they get tagged, and any drift is reported by the script. (I don't have a mechanism to have the drift notice show up on the website when due to drifted includes. I'll have to think about that.)