Support labels from values.yaml

[KatieBSC]

I'm getting started using yatai and am deploying with Helm. The issue that I've run into is that currently it's not possible to define labels from a values.yaml file, since "yatai.labels" are defined in the _helpers.tpl and don't reference values.

It would be great to have the option to declare common labels in the values file and have these values sourced in the helpers template. 🙏