enclose YAML strings containing % with quotes

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #4029

Thanks @iamdto, did you spot some other occurences in the docs?
That's true. I didn't look carefully enough.This change is now reverted.

For the JSON example: It's not rendered properly because of the ``...`` the JSON is no longer valid. Though I'm not sure how to work with that.