Docs: Logstash 8.16.0 release docs

[karenzone]

Logstash release manager: @edmocosta
Logstash tech writer: @karenzone
Docs release manager: @lcawl

Logstash release docs

• Day after FF, cut branches:
  • logstash
  • logstash-docs
  • ingest-docs
    • Update backport tooling for ingest-docs: Add 8.16 branch to backport and mergify configs ingest-docs#1385
    • Update backport labels:
• Release notes: Release notes for 8.16.0 #16605
  • Add link to docs release issue: https://github.com/elastic/dev/issues/2724
  • Verify that release notes PR is forwardported to 8.x: Backport PR #16605 to 8.x: Release notes for 8.16.0 #16662
• Update plugin docs: updated docs for 8.16 logstash-docs#1749
  • Bump lock file: Add lockfile from 8.15 branch #16561

Add known issue and realign

• Doc: Realign release notes and add known issue #16663

Special considerations

• Impact of Health API in 8.16.0 - what to expect on a comparison with previous versions