Accept target version in Rollback

[AgustinRamiroDiaz]

The helm internal method for running the rollback
https://github.com/helm/helm/blob/bed23120b048977d67c929cec915e1d6e0887c5d/pkg/action/rollback.go#L58

takes into account the version from the struct
https://github.com/helm/helm/blob/bed23120b048977d67c929cec915e1d6e0887c5d/pkg/action/rollback.go#L108

which through the helm cli is getting injected at almost top level, when running the command
https://github.com/helm/helm/blob/bed23120b048977d67c929cec915e1d6e0887c5d/cmd/helm/rollback.go#L66

Currently, I did not find a way to modify this value to have a rollback to a particular version. I found that we can overcome this easily by adding the version as a parameter in rollbackRelease.

If there's no alternative way, and you like my proposal, I can work on the fix :D

Other questions that arise are how should the other fields get set? Currently they get inherited from creation, and the helm CLI does something similar.

[AgustinRamiroDiaz]

BTW nice client!