Doc: Logstash 8.16.6 release docs

[karenzone]

Logstash release manager: @andsel
Logstash tech writer: @karenzone
Docs release manager: @natasha-moore-elastic

Logstash release docs

• Release notes: Release notes for 8.16.6 #17378
  • Add link to docs release issue: https://github.com/elastic/dev/issues/3072
  • Verify that release notes PR is forwardported to 8.x, 8.18, 8.17:
• Update plugin docs: updated docs for 8.16 logstash-docs#1822
  • Bump lock file