zFTP: Inconsistent error messages on functionality yet to be implemented

[zFernand0]

Describe the bug

The error message that appears when a functionality is not implemented on the zFTP VSCE is quite different from operation to operation.

To Reproduce

Attempt any of the following operations:

1. Download All Spool (Binary) (it lets you select the directory before failing)
2. Get JCL
3. Download Single Spool
4. Issue Stop Command

Expected behavior

To have a consistent error which ideally comes from the zFTP extension and not ZE

Screenshots

Desktop (please complete the following information):

• OS: Any
• Zowe Explorer Version: latest
• (Optional) Zowe CLI Version: N/A
• (Optional) Are you using Secure Credential Store? N/A

Additional context

The order of the errors match the order of the operations listed above (in the reproduce section)

[github-actions[bot]]

Thank you for creating a bug report. We will investigate the bug and evaluate its impact on the product. If you haven't already, please ensure you have provided steps to reproduce the bug and as much context as possible.

[JTonda]

Investigate implementing a common error type for extenders which they can extend and ze can format the output.