feat: yaml output

[kimskimchi]

Summary

Introduces yaml for existing json outputs.
Comes with free tests. 👍

Checklist

• Wrote appropriate unit tests
• Considered security implications of the change
• Updated associated docs where necessary
• Updated associated configuration where necessary
• Change is backwards compatible if it needs to be (user can upgrade without manual steps?)
• Nothing sensitive logged
• Considered data migrations for smooth upgrades

Related Issues

Resolves #972

[BruceMacD]

Any way we could have a re-usable function for the output formatting to reduce the repetition in the cli output code here?

[mxyng]

Mentioned in the previous change. There should be a Formatter interface which JSON/YAML/TableFormat implements. The result is passed to cli.Output for printing. This will allow more formats to be added with minimal impact on the existing code base

[kimskimchi]

For the actual function, not sure how this can be achieved, could I have an example?

The couple of commands here are all list, so it expects similar outputs, but different functions will not use the same something.Items but rather be completely different.

[dnephin]

Since yaml.Marshal and json.Marshal can accept anything, the function would can accept an argument of type interface{}. The one challenge is the table format, since that requires a bit more guidance to tell it which columns to use.

I think we could do this as a follow up.

[dnephin]

I put together an example of one option here: cli-9...dnephin/formatter-example

But let's look into that in a follow up PR.

[dnephin]

Looks good. We should move the Conencted provider output to Stderr, but otherwise this looks great. I think we can refactor to a formatter interface in a follow up.

[dnephin]

Since yaml.Marshal and json.Marshal can accept anything, the function would can accept an argument of type interface{}. The one challenge is the table format, since that requires a bit more guidance to tell it which columns to use.

I think we could do this as a follow up.

[dnephin]

For anyone else curious about this. It turns out we have to use sigs.k8s.io/yaml so that the field names come from the json tags. If we used the more standard yaml library we'd have to add yaml names to all the fields, and the output would look strange for some fields (ex: would use {} for the zero value of api.Time instead of null).

Although the second part of that we could fix by changing to MarshalText instead of MashalJson.

[dnephin]

I put together an example of one option here: cli-9...dnephin/formatter-example

But let's look into that in a follow up PR.