Fall back to gzip when missing optional zopfli dependency

What does this MR do?

Addresses omnibus-gitlab#2454 (closed) by wrapping zopfli compression in a try/catch block so that the frontend assets can still be compiled on systems where zopfli is not available.

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?

omnibus-gitlab#2454 (closed)