Should File Loader Fail if Directory Doesn't Exist?

Previously, we allowed Weave to be configured using Mix.Config, which allowed per environment configuration.

This allowed production to consume a directory, such as /run/secrets and development to only use the environment loader. This now isn't possible, unless you use conditional invocation; which we'd not recommend.

This isn't a problem, except the directory may not exist in development.

I'm proposing that the directory not existing should be skipped, and further use of required: true within the config should enforce keys to be loaded.