[Bug]: All backends using `gpt-3.5-turbo` as default model

[gyliu513]

Checklist

• [X] I've searched for similar issues and couldn't find anything matching
• [X] I've included steps to reproduce the behavior

Affected Components

• [X] K8sGPT (CLI)
• [ ] K8sGPT Operator

K8sGPT Version

v0.3.38

Kubernetes Version

v1.30

Host OS and its Version

No response

Steps to reproduce

gyliu@guangyas-air k8sgpt % ./bin/k8sgpt auth add --backend watsonxai
Warning: model input is empty, will use the default value: gpt-3.5-turbo
Provider with same name already exists.

gyliu@guangyas-air k8sgpt % ./bin/k8sgpt auth add --backend localai
Warning: model input is empty, will use the default value: gpt-3.5-turbo
localai added to the AI backend provider list

From above, we can see both watrsonxai and localai settinng gpt-3.5-turbo as default model, this is not right.

Expected behaviour

Each LLM backend should have its own default model

Actual behaviour

No response

Additional Information

No response