Render defaults as yaml when using --example-format yaml

Hey,
Pretty much as the title says we use `--example-format yaml` for the examples, but the defaults are still rendered as json. It'd be good if these were rendered as yaml too.

The issue does not identify a file, test, or entry point. Start by locating the handling for --example-format and the rendering of defaults, then check how JSON and YAML examples are generated. Done means defaults use YAML whenever --example-format yaml is selected, while other formats retain their existing behavior.

Written by the indexing model from the issue text.