[CI] Refactor OTel-Java related front-matter version keys + autoupdate script changes

[chalin]

• Contributes to:
  • Preparation for Add documentation on the OTel Spring Boot starter #3377
  • CI/infra improvements - 2023/11 #3458
• Refactors the OTel-Java related front-matter version keys so that they are all in docs/instrumentation/java/_index.md. This enables all pages in that section to access the variables
• Renames the variables so that they are shorter, given the context. I.e., for pages under the Java section, vers.semconv means the version of Java semconv, etc.
• There are no changes to the generated site files (modulo timestamps etc):

  $ (cd public && git diff) | grep ^diff 
  diff --git a/docs/instrumentation/java/automatic/annotations/index.html b/docs/instrumentation/java/automatic/annotations/index.html
  diff --git a/docs/instrumentation/java/exporters/index.html b/docs/instrumentation/java/exporters/index.html
  diff --git a/docs/instrumentation/java/index.html b/docs/instrumentation/java/index.html
  diff --git a/docs/instrumentation/java/manual/index.html b/docs/instrumentation/java/manual/index.html
  diff --git a/docs/instrumentation/java/resources/index.html b/docs/instrumentation/java/resources/index.html
  diff --git a/site/index.html b/site/index.html
  diff --git a/sitemap.xml b/sitemap.xml
  $ (cd public && git diff -I 'dateModified|lastmod|modified_time|Last modified') | grep ^diff               
  diff --git a/site/index.html b/site/index.html

[chalin]

For the record, I just tested the updated action, and it runs fine (when there are no updates); see, https://github.com/open-telemetry/opentelemetry.io/actions/runs/6774462331/job/18411562909.