docs migration - Deploying on Ubuntu

Source: documentation/server/guides/deploying/ubuntu.md
Proposed disposition: Migrate
Proposed destination: server-guides/Sources/ServerGuides.docc/deploying/ubuntu.md
Reviewer: @swiftlang/server-workgroup

Checklist

• Create a GitHub issue to track this migration
• Determine disposition (suggested: Migrate) and confirm destination
• Review source for accuracy against current Ubuntu LTS releases supported by Swift
• Translate Jekyll markdown to DocC markdown format
  • Remove YAML front matter
  • Convert any Jekyll callouts to DocC-style callouts
  • Update cross-references to the DigitalOcean guide to use DocC links
  • Verify all shell commands against current Ubuntu setup
• Add article to ServerGuides.docc/Documentation.md under a "Deployment" topic group
• Run swift package generate-documentation --analyze --warnings-as-errors in server-guides/
• Preview locally with swift package --disable-sandbox preview-documentation in server-guides/
• Submit PR to this repository for server workgroup review
• After merge and publication: add redirect_to: in the swift.org source file's front matter
• Submit redirect PR to swift-org-website

Start with documentation/server/guides/deploying/ubuntu.md and compare it with current supported Ubuntu LTS releases. Migrate it to server-guides/Sources/ServerGuides.docc/deploying/ubuntu.md, add it to ServerGuides.docc/Documentation.md, and run the listed documentation generation and preview commands in server-guides/. Done includes workgroup review and the post-publication redirect updates described in the checklist.