Docs: Logstash 8.15.5 release docs

[karenzone]

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

Logstash release docs

• Release notes: Release notes for 8.15.5 #16693
  • Add link to docs release issue: https://github.com/elastic/dev/issues/2886
  • Verify that release notes PR is forwardported to 8.x:
  • Verify that release notes PR is forwardported to 8.17: Forward port 8.15.5 and 8.16.2 release notes to 8.17 #16810
  • Verify that release notes PR is forwardported to 8.16:
• Update plugin docs: updated docs for 8.15 logstash-docs#1759
  • Bump lock file: bump lock file for 8.15 #16692