Add optional model-family attributes and call to Claude to code generation endpoint

Problem to solve

We want to be able to choose from outside to which model the code generation request is routed

Proposal

model-family (feel free to find a better name)

Optional, To specifically select a model family (we would still control the version in the model gateway)

Default is code-gecko and claude is possible.

If the model-family is claude we then need to route that call to Anthropic Claude https://docs.anthropic.com/claude/reference/getting-started-with-the-api. There is already an MR in progress to add anthropic as proxy endpoint to enable Chat - with which we need to coordinate - !383 (closed)

Further details

Links / references