Fleet and Agent 8.19.5 release notes

[karenzone]

Docs release manager: @nastasha-solomon
Tech Writer: @karenzone
Docs release issue: https://github.com/elastic/dev/issues/3311

Fleet and Agent release notes

• Release notes PR: Doc: Add Fleet and Agent release notes for 8.19.5 ingest-docs#1863
  • Add PR link to docs release issue

Content source (merge not required)

• Agent: Changelog for 8.19.5 elastic-agent#10263
• Fleet: NO CHANGES

No backports required

Docs preview: https://ingest-docs_bk_1863.docs-preview.app.elstc.co/guide/en/fleet/8.19/release-notes-8.19.5.html