Remove our yaml hacks by switching to goccy/go-yaml lib.

Recently we have trouble customizing marshalling of 3rd party structs like:

* Prometheus omitzero problem that cause us to copy structs which is hard to sustain https://github.com/GoogleCloudPlatform/prometheus-engine/pull/1555#issue-2955046159
* Alertmanager secret redaction hacks https://github.com/GoogleCloudPlatform/prometheus-engine/pull/1562

I think we coud replace those frictions by replacing gopkg.in/yaml with https://github.com/goccy/go-yaml?tab=readme-ov-file#features

Another reason for this work is that [`gopkg.in/yaml.*` project seems to be deprecated](https://github.com/go-yaml/yaml?tab=readme-ov-file#this-project-is-unmaintained).