This finishes the work started at #1619 by introducing the following changes:
- You can now set `HELMFILE_TEMPDIR` and `CHARTIFY_TEMPDIR` as the directory to persist temporary values files rendered by helmfile and temporary charts generated by chartify. Note that chartify is used internally when you use kustomize integration or raw K8s manifests as a chart.
- Helmfile uses the hash sum of the release config and the values file content in the file name of the temporary values file.
In combination with `HELMFILE_TEMPDIR` and `CHARTIFY_TEMPDIR`, this enables helmfile to use the stable file names for temporary values files, which contribute to stabilize log messages like `Comparing release=appset, chart=PATH/TO/TEMPORARY/CHART`, where the `PATH/TO/TEMPORARY/CHART` had been randomized due to formerly random helmfile tempdir and temporary values file names, and random chartify tempdir.
You can try this feature with a script like:
```
tempdir=$(mktemp -d -t helmfile)
HELMFILE_TEMPDIR=${tempdir} CHARTIFY_TEMPDIR=${tempdir} helmfile diff
rm -rf ${tempdir}
```
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