`--retain-values-files` prevents temporary values files that were passed to Helm commands run by Helmfile for debugging purpose.
With that, you can manually rerun helm commands that were logged when `--log-level=debug` is enabled.
Resolves ##1117
The addition of `--set k1=v1,k2=v2` and `--values file1 --values file2` was originally planned in #361.
But it turned out we already had `--values` for existing helmfile commands like `sync`. Duplicated flags doesn't work, obviously.
So this actually add `--state-values-set k1=v1,k2=v2` and `--set-values-file file1 --set-values-file file2`.
They are called "state" values according to the discussion we had at #640Resolves#361
KUOKA Yusuke