Logstash 8.19.4 release docs

[karenzone]

Docs release manager: @kosabogi
Logstash release manager: @donoghuc

Logstash release notes

• Logstash release notes PR: Release notes for 8.19.4 logstash#18157
• Add PR link and Logstash RM to docs release issue: https://github.com/elastic/dev/issues/3280

Logstash plugin docs

• Bump lock file
• Update plugin docs: updated docs for 8.19 logstash-docs#1907