investigate + implement decoupling legacy helm deployer to use the helm renderer

Currently in Skaffold V2 @ HEAD, skaffold has 2 "modes" for helm that require different schema configurations:

- helm renderer + kubectl deployer schema config
```
TODO
```

- legacy helm deployer
```
TODO
```

while this is likely somewhat confusing to users writing this schemas themselves (as to which to use and the difference between them), skaffold fix currently only supports generating schemas with the legacy helm deployer syntax.

This issue tracks possibly changing the LegacyHelmDeploy to take information from the `manifests` field and potentially work more similarly to a `Deployer` vs a `Renderer+Deployer`