Renovate: Helmfile Manager should update Lockfile

[Preisschild]

What would you like Renovate to be able to do?

The new Helmfile Manager currently only updates the version in the helmfile.yaml, but doesnt update the version and a sha256 digest in the helmfile.lock file thats next to helmfile.yaml

Did you already have any implementation ideas?
The issue could be solved by installing Helmfile inside the Dockerfile and add a postUpdateOption that executes helmfile deps and commites those changes.

Are there any workarounds or alternative ideas you've tried to avoid needing this feature?
executing helmfile deps yourself and commit those changes in the MR branch

[rarkins]

A solution similar to #7641 would be best. We'd also need to add helmfile to https://github.com/renovatebot/docker-buildpack