Resolve "9.0 upgrade documentation should include Yarn"

What does this MR do?

Adds yarn:install rake task to the upgrade documentation to replace the old call to npm install --production. This rake task should handle installing locked frontend dependencies and gracefully failing with useful error messages if the user does not have yarn installed on their system.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• [ ] Changelog entry added, if necessary
• Documentation created/updated
• [ ] API support added
• Tests
  • [ ] Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #29730 (closed)