Use zopfli for better asset compression and disable compression in CI

What does this MR do?

Uses zopfli to compress assets, resulting in ~7.2s smaller bundles but a 70% longer compile time. Disables compression in the rake gitlab:assets:compile CI step.

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

Need to test this in the omnibus build suite to ensure it doesn't add an excessive burden on our compile process.

Why was this MR needed?

Smaller bundle sizes transmitted over the network yield faster load times to the end user, especially on slow connections.

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 #32992 (closed)