Pulumi-kubernetes: Support Helm 3

[hausdorff]

Helm 3 will probably be released before KubeCon NA this year. We should make sure to support it on day 1. For extra credit, it might be worth breaking it out into its own provider.

Largely the helm 3 command line remains the same. There are some breaking changes, but our current understanding, having looked at the beta releases, is that our general strategy should be about the same: shell out to the helm CLI to expand templates, apply.

We'll use this issue to track the work required to implement this.

[joeduffy]

@lblackstone @lukehoban Putting in M30, but would be good to take an early look at this as soon as the other stuff is out the door this week, to understand whether this "just works" or not.

[frank-bee]

@hausdorff do you plan to use the templating mechanism only of helm3 or even installing the charts with helm3? Since helm3 is tillerless, why not installing directly to the make sure to have the very same behavior with pulumi than you would have with helm3 itself?

[nesl247]

FYI helm 3 launched today.