Related to #782 and #444
- Allows concurrent decryption of different secrets files
- Caches decrypted secrets by original file path and returns decrypted results from memory
- Secrets being run through an instance of helmexec will be cached and run as fast as possible concurrently
NB: This particular PR doesn't make _all_ calls to secrets cached and concurrent. Environment Secrets in particular seem to not be evaluated with a ScatterGather(), and doesn't use the same helmexec instance as other parts of the code, so it doesn't take advantage of these changes. Some reworking of the plumbing there would be needed.
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.