Write log/error output from commands to stderr. (#1632)

- Closes #1631.
- The standard output should only contain result data,
  so that scripts consuming stdout don't need to scrape.

Sources/ContainerCommands/Image/ImageDelete.swift

@@ -82,7 +82,7 @@ extension Application {
             let freed = formatter.string(fromByteCount: Int64(size))
 
             if didDeleteAnyImage {
-                print("Reclaimed \(freed) in disk space")
+                log.info("Reclaimed \(freed) in disk space")
             }
             if failures.count > 0 {
                 throw ContainerizationError(.internalError, message: "failed to delete one or more images: \(failures)")

Sources/ContainerCommands/Image/ImageLoad.swift

@@ -108,7 +108,6 @@ extension Application {
             }
             await taskManager.finish()
             progress.finish()
-            print("Loaded images:")
             for image in result.images {
                 print(image.reference)
             }

Sources/ContainerCommands/Image/ImagePrune.swift

@@ -82,7 +82,7 @@ extension Application {
             let formatter = ByteCountFormatter()
             formatter.countStyle = .file
             let freed = formatter.string(fromByteCount: Int64(size))
-            print("Reclaimed \(freed) in disk space")
+            log.info("Reclaimed \(freed) in disk space")
         }
 
         private func hasTag(_ reference: String) -> Bool {

Sources/ContainerCommands/Image/ImageSave.swift

@@ -84,7 +84,7 @@ extension Application {
                 do {
                     images.append(try await ClientImage.get(reference: reference, containerSystemConfig: containerSystemConfig).description)
                 } catch {
-                    print("failed to get image for reference \(reference): \(error)")
+                    log.error("failed to get image for reference \(reference): \(error)")
                 }
             }