[python-fastapi] Use ... as default value rather than None (#22494)

[zhornback]

With various FastAPI parameters (Query, Path, Header, Cookie, Body, Form, and File) the default value of None is a valid value, but signifies that the parameter is optional. To allow for required parameters, default should either not be set at all or be set to '...' (ellipsis).

Reproduction details can be found in #22494.

fixes #22494

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---

Summary by cubic

Switch the python-fastapi generator to emit ... for required params and None for optional ones so FastAPI enforces OpenAPI required semantics. Updates tests and regenerated samples; fixes #22494.

• Bug Fixes

  • Simplify endpoint_argument_definition.mustache to use ... when required, else None, across Query, Path, Header, Cookie, Body, Form, and File.
  • Update tests to expect Body(...) and required Form(...); regenerate petstore samples accordingly.

• Dependencies

  • In kotlin-spring-cloud-4 sample: bump Jackson 3 from 3.1.0 to 3.1.5 for tools.jackson.* artifacts, and update Gradle wrapper to 8.14.5.

^{Written for commit 4fe0d0d. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 4 files

[darkobardic]

@zhornback, thanks for this — filed the original issue #22494 and your fix works correctly against our python-fastapi server (Query(...) for required, 422 on missing params).

Any chance you could rebase? The conflict looks like just regenerated samples, and the circleci: node2 failure looks flaky (sharded runner, all ~15 other checks green).

[zhornback]

Looks like some bitrot set in. Looking into it.

[darkobardic]

Thanks @zhornback!

@wing328, would you mind taking a look when you have a moment? Small python-fastapi fix for #22494. Thanks!

[wing328]

please resolve the merge conflicts and i'll try to get it merged into upcoming release (v7.25.0) 🙏

[zhornback]

@wing328 I have resolved the merge conflicts and adjusted new tests. Tests are passing.

Tag you're it.