### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

Calling /key/generate with the same secret key as an existing one doesn't throw an error. While it is probably not too likely that this happens to someone, it should still return an error.

### Steps to Reproduce

1. Call /key/generate with ``` { "key_alias": "test duplicate" } ``` 2. Call it again (replace placeholder) ``` { "key_alias": "test duplicate 2", "key": "[placeholder for value of "key" from previous response]" } ``` 3. Only the first key exists now although second response returned 200 and also the correct name

### Relevant log output

```shell 1st response:

{ "key_alias": "test duplicate", "duration": null, "models": [], "spend": 0.0, "max_budget": null, "user_id": null, "team_id": null, "max_parallel_requests": null, "metadata": {}, "tpm_limit": null, "rpm_limit": null, "budget_duration": null, "allowed_cache_controls": [], "config": {}, "permissions": {}, "model_max_budget": {}, "model_rpm_limit": null, "model_tpm_limit": null, "guardrails": null, "prompts": null, "blocked":…