Add confetti to certificate congrats page

[Hamms]

Follow-up to #34451

Adds some confetti to the certificate congrats page upon personalization!

Open Question

Currently, this only affects the page at studio.code.org/congrats, not the page at code.org/congrats. It's not super clear to me why we still have both of these, but the latter one doesn't currently support React. Rather than trying to add this functionality to that page, I'd suggest the best thing to do would be to just combine these two pages into one. That would of course be more work in the short term than would just adding this feature to both pages, but would of course be better in the long term.

So, are there any objections or concerns to just adding this confetti to one of the congrats pages for now?

Testing story

Tested manually, relying on existing unit tests for long-term testing.

Reviewer Checklist:

• Tests provide adequate coverage
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[Erin007]

I don't have any concerns about confetti only being on studio.code.org/congrats. LP-450 tracks the work of consolidating the pegasus and dashboard versions; but, it's been a long uphill battle to prioritize. I would be thrilled to see us tackle this before this year's Hour of Code.

[Erin007]

Thank you! This makes the congrats page feel so much more fun!