upgrade to yaml.v3

[wadey]

The main nice fix here is that maps unmarshal into map[string]any instead of map[any]any, so it cleans things up a bit.

The only gotcha I see for our uses is that the Yaml 1.1 bool types like yes won't automatically be set as a bool inside of map[string]any. So I added a little helper config.AsBool to keep backwards compat there.

• https://ubuntu.com/blog/api-v3-of-the-yaml-package-for-go-is-available