Use schema.example values instead of schema.default in API playground pre-fill

[vollmarj]

Description:
The API playground currently uses schema.default values to pre-fill request parameters, which creates a poor UX when developers want to quickly test endpoints. This forces documentation authors to choose between two bad options:

1. Set incorrect "default" values just to make the playground work
2. Leave the playground with empty/invalid parameters that require manual input

Proposed Solution:
Change the API playground to prioritize schema.example values over schema.default values when pre-filling request parameters. This would allow developers to hit "play" and immediately send a valid request with meaningful test data.

Expected Behavior
When both schema.example and schema.default exist, use schema.example for playground pre-fill
Fall back to schema.default only when no example is provided
This maintains semantic correctness while improving the testing workflow

Current Behavior
The playground displays schema.default values as implemented in #1065, which prioritizes showing actual default values rather than example values.

Impact
This change would significantly improve the developer experience by enabling one-click API testing with realistic data while maintaining proper OpenAPI schema semantics.

[mosch]

Hey @vollmarj great writeup, thanks for that. We've discussed this multiple times as well. We've seen many APIs that use invalid, non-working values in their sample values. They look at them more as the "placeholder" in the tag rather than the default value.

I think we'd need to come up with two things here:

1. Let users choose what values to use
2. Decide on the best default behavior.

[picsoung]

Found this issue as I was trying to understand why zudoku was not picking my example in the Response but instead generating from schema.

Would be cool to support it for those that spend time providing real examples.