Update gopkg.in/yaml.v2 to gopkg.in/yaml.v3

[tklauser]

API v3 was released in 2019 [1]. Update from the v2 API, no changes to the packages's use needed and no breaking changes expected.

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

[jpmcb]

I'd like to take a look at this and quickly compare some diffs of docs generated via v2 and v3 - but we should be able to get this in with no problem!

[umarcor]

@marckhouzam please milestone this as well!