feat: add claude 3.7 code generation support

What does this merge request do and why?

Adds code generation template for the new Claude 3.7 Sonnet model

Resolves gitlab-org/gitlab#521045 (closed)

How to set up and validate locally

curl -X "POST" "http://gdk.test:5052/v3/code/completions" \
     -H 'Content-Type: application/json; charset=utf-8' \
     -d $'{
  "prompt_version": 3,
  "prompt_components": [
    {
      "type": "code_editor_generation",
      "payload": {
        "prompt_version": "3.0.2-dev",
        "model_name": "base",
        "file_name": "main.go",
        "content_above_cursor": "func parseEnvFile(filename string) (map[string]string, error) {",
        "prompt_id": "code_suggestions/generations",
        "prompt_enhancer": {
          "user_instruction": "hello world"
        },
        "content_below_cursor": "}",
        "language_identifier": "go"
      }
    }
  ]
}'

Merge request checklist

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