Fix 8.17 upgrade documentation

What does this MR do?

Updates documentation for upgrading from GitLab 8.16 to 8.17 (non-omnibus method) to ensure users are running the required minimum version of NodeJS and that they have installed the required node modules prior to compiling gitlab assets.

Also adds a line in the upgrader.rb script to perform npm install --production prior to compiling assets.

Note: this MR previously was set up to add information about yarn and create helpful error messages in gitlab rake tasks to point out errors in a user's dependencies, but this has been moved to a separate MR as yarn support has been pushed back to %9.0

Does this MR meet the acceptance criteria?

• Changelog entry added
• 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 #28021 (closed)