Fix broken links from APM-Server 10874

[kilfoyle]

This is an attempt to fix some broken links in the current docs build:

08:57:42 INFO:build_docs:  /tmp/docsbuild/target_repo/html/en/apm/agent/nodejs/3.x/agent-api.html contains broken links to:
08:57:42 INFO:build_docs:   - en/apm/guide/8.8/metadata-api.html#metadata-schema
08:57:42 INFO:build_docs:  /tmp/docsbuild/target_repo/html/en/apm/agent/nodejs/current/agent-api.html contains broken links to:
08:57:42 INFO:build_docs:   - en/apm/guide/8.8/metadata-api.html#metadata-schema
08:57:42 INFO:build_docs:  /tmp/docsbuild/target_repo/html/en/apm/agent/nodejs/master/agent-api.html contains broken links to:
08:57:42 INFO:build_docs:   - en/apm/guide/8.8/metadata-api.html#metadata-schema

The change would need to be backported from main and 3.x.

[kilfoyle]

@elasticmachine run elasticsearch-ci/docs

[kilfoyle]

Closing. The build is fixed using redirects via elastic/apm-server#10891