Log missing configuration files

Once Environment providers allow for ignoring missing config files, they should probably log something when the file is not found.
It might be a user-error that the file isn’t there and this would be hard to detect otherwise.

Start by tracing the Environment providers and their handling of missing configuration files, especially the path used when missing files are ignored. Check the existing provider behavior and tests, then define completion as emitting a log when an ignored configuration file is not found without changing the loading result.

Written by the indexing model from the issue text.