Helm 4: Refactor/feature: Modernize Helm SDK API and better CLI/SDK separation

[gjenkins8]

Helm's SDK was quickly created to satisfy a need for users to utilize Helm programatically. Unfortunately, as a nascent effort, the SDK wasn't cleanly separated from the CLI. And over time, the SDK has grown various warts and oddities for SDK users.

For example, using the install action looks somewhat like:
https://helm.sh/docs/sdk/examples/#install-action
https://helm.sh/docs/sdk/examples/#driver

This issue is to get started with how improving the SDK can be done. Goal is to write a (Helm 4) HIP for January and make improvements for Helm 4.

[gjenkins8]

Working from the other side, #384 considers what APIs might be made private (internal)