Remove need for Helm `artifactsOverride` by using Skaffold as a post-renderer

[briandealwis]

Helm 3.1 supports specifying a post-renderer, a simple filter that is afforded an opportunity to alter the rendered manifests prior to being applied to the cluster. We use the post-renderer to support skaffold debug with Helm (#4732). We should use the post-renderer as part of the helm install and helm upgrade to perform our manifest transformations more generally and thus side-step the need for artifactsOverride and our separate labelling step. This change would greatly simplify configuration of Helm projects as well as avoiding resource churn (e.g., setting a label on a deployments will re-create its pods; #3133).

This change will require moving our minimum supported Helm version to 3.1.0.

• [x] Remove artifactOverrides and use Helm's post-renderer to call back into Skaffold to hydrate the Helm-rendered manifests (#6949)
• [ ] Transition users using artifactOverrides (#6952)
• [ ] Add support for subsequently invoking user-configured post-renderers via deploy.helm.flags (#6951)

[tejal29]

@briandealwis are you planning to get this in ?

[briandealwis]

Yes. Hit some stumbling blocks with testing.

[tejal29]

@briandealwis Is this done on v2?

[briandealwis]

#6951 and #6952 are still outstanding