Adds paths to secrets in resourcex.Unmashal result

[danielrbradley]

Currently, Unmarshall only includes the bool value ContainsSecrets. If we could also include a list of paths which contain secrets then we could use this metadata to accurately reconstruct the secrets through a matching Marshal method.

This property could be called SecretPaths and be of type []resource.PropertyPath where each string is a path to the property value in the property map e.g. prop.subProperty.

See also:

• Add resourcex.Marshal #200