Add /api/racer endpoint

[Anupya]

Description

• Implement create_race = /api/racer endpoint.
• Rename id to more clear puzzle_id since id shadows the built-in id (could be breaking 🚨)
• Rename max to max_entries since max shadows the built-in max (could be breaking 🚨)
• high score is two words!

After merge

Please check off /api/racer in issue description #6.

[benediktwerner]

I don't think it's worth changing the parameter names given that it could be a breaking change.

And as mentioned in #50, ideally the return types of new endpoints should be typed using TypedDict.

[kraktus]

Thanks!