Fix OAS file in YAML format is not formatted after hydration

[edenreich]

Summary

After running hydration the environment variables are being saved to the OpenAPI Spec, but the formatting of the document seems off.

The serde_json crate seems to have pretty print, but the serde_yaml crate don't for whatever reason - a little bit inconsistency there.

This has to be addressed preferably without too many dependencies, previously I used prettier, but it would be maybe better without it if possible.