[Improvement] Support function command in CLI

### What would you like to be improved?

Support function command in CLI

### How should we improve?

Add a new `function` command to the CLI.

The command should provide function-related operations, such as listing, showing, or managing functions through the CLI, so users can operate functions directly without calling the REST API manually.

The expected improvement is to make function management consistent with other CLI resources and provide a more convenient user experience.