generate-values: don't use relative path for helmfile

[tarrow]

Describe the changes

We think that this fails when running from a place other than the root of this repo.

We saw it error with error: helmfile not found: 'k8s/helmfile/helmfile.yaml' when trying to call this from and action in the ui repo.

Prior discussion

Pair programmed with @deer-wmde

[tarrow]

Abandoned because this doesn't actually work well using a helmfile in docker type situation