fix: broken .retrieve call using identifier=

[cdoern]

What does this PR do?

identifier is not a valid argument for retrieve but model_id is.

╰─ llama-stack-client models get meta-llama/Llama-3.2-3B-Instruct
╭────────────────────────────────────────────────────────────────────────────────────╮
│ Failed to get model details                                                        │
│                                                                                    │
│ Error Type: TypeError                                                              │
│ Details: ModelsResource.retrieve() got an unexpected keyword argument 'identifier' │
╰────────────────────────────────────────────────────────────────────────────────────╯

Test Plan

the error now is:

╰─ llama-stack-client models get meta-llama/Llama-3.2-3B-Instruct
╭────────────────────────────────────────────────────╮
│ Failed to get model details                        │
│                                                    │
│ Error Type: NotFoundError                          │
│ Details: Error code: 404 - {'detail': 'Not Found'} │
╰────────────────────────────────────────────────────╯

[yanxi0830]

Thanks!

Filed an issue separately to address your new error: meta-llama/llama-stack#1038