helm-secrets uses the `HELM_SECRETS_DEC_SUFFIX` env var to define the name of the output file
we should have the same logic in helmfile, to come up with the same filename
It only affects people using the `HELM_SECRETS_DEC_SUFFIX` env var
Use-case: if you want to run multiple `helmfile` commands in parallel, without conflicts. in this case, you need to decrypt secrets with different suffixes.
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