* [C] Don't convert post body strings to JSON
If the body provided for the api request is a just a string itself,
don't try to convert it to JSON, simply submit the string.
* [C] Implement BearerToken authentication
* [C] Handle nullable fields correctly
* [C] Fix implementation of FromString for enums
* [C] Update the test schemas to cover the changes
* Update samples
* Fix the updated samples
* [C] Add the new samples folder to the CI workflow
