Create base prompt template for code generation with Anthropic

We want to add in parallel to the current google based code generation path a new way for doing code generation based on Anthropic. Which means we need to have the additional option to do code generation with Claude, which needs its own specifically rewritten template based on the already existing one which was introduced in #424343 (closed)

• We want to steer traffic based on Feature flags.
• The model gateway will be extended with an attribute model-family so it knows where to direct the premade prompt to