Cache output of sops decrypt in memory to improve performance
Cache output of sops decrypt in memory to improve performance

When sops is used with PGP smartcards, each decrypt operation can take
3-10 seconds.

This commit adds an in memory cache that ensures terragrunt only
decrypts a file once during an invocation.

fixes #1343

gruntwork-io/terragrunt,gruntwork-io/terragrunt