feat: use codellama:code for code completions

What does this merge request do and why?

Code-Llama has a dedicated model for completions, thus register its code variant to be used for code completions.

In order to allow codellama to be used for both generations and completions, the litellm config would look like this:

model_list:
  - model_name: codellama
    litellm_params:
      model: ollama/codellama:13b
      api_base: http://localhost:11434
  - model_name: codellama:code
    litellm_params:
      model: ollama/codellama:13b-code
      api_base: http://localhost:11434

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.