Enhance logging for SFTP error handling

[skxeve]

Currently, when an SftpDownload operation fails, the log only shows a brief message: "SFTP failed." This makes troubleshooting difficult because you have to check the configuration to figure out the username, destination host, and authentication method used. To improve this, we'd like to make the log more detailed.

Although not individually confirmed, it's possible that similar issues exist in other related SFTP processes, such as SftpUpload.

[skxeve]

For this issue, we consider the fix for SFTPDownload to be mandatory.
While fixes for other similar classes (e.g. SFTPUpload) would be better, they can be prioritized later.