Write all logging (INFO, WARN, ERROR) to stderr

The old setup tried to log >= warning to stderr, the rest to stdout.

However, that logic was flawed, so warnings ended up in stdout, which makes `hugo list all` etc. hard to reason about from scripts.

This commit fixes this by making all logging (info, warn, error) log to stderr and let stdout be reserved for program output.

Fixes #13074

deps/deps.go

@@ -405,9 +405,11 @@ type DepsCfg struct {
 	// The logging level to use.
 	LogLevel logg.Level
 
-	// Where to write the logs.
-	// Currently we typically write everything to stdout.
-	LogOut io.Writer
+	// Logging output.
+	StdErr io.Writer
+
+	// The console output.
+	StdOut io.Writer
 
 	// The file systems to use
 	Fs *hugofs.Fs