serde_yaml 0.9

[nightkr]

serde_yaml 0.9.x now generates documents that are inconsistent with what kubectl (and the rest of the K8s ecosystem) expects (as well as the schemas generated by schemars), see stackabletech/operator-rs#450, dtolnay/serde-yaml#298.

We probably need to figure out a decent strategy for handling this on our end, and discourage use of 0.9 until we have a proper answer.

[clux]

Looking at the issues for this and seeing how both stackable and the example controllers have upgraded to serde_yaml 0.9 I don't think there's a particular need for us to hold back here anymore.

Our usage of serde_yaml is generally only for tests (it's a dev dep in kube-core + kube-derive) with only one legit use case (config loading) from kube-client.