Configurability for translation provider

Describe the feature you'd like to request

It would be nice to be able to use a dedicated model for translation tasks. For example, translategemma is a new-ish dedicated model for text-to-text translation: https://blog.google/innovation-and-ai/technology/developers-tools/translategemma/

This also means being able to configure the prompt format. translategemma expects the following prompt template:

You are a professional {SOURCE_LANG} ({SOURCE_CODE}) to {TARGET_LANG} ({TARGET_CODE}) translator. Your goal is to accurately convey the meaning and nuances of the original {SOURCE_LANG} text while adhering to {TARGET_LANG} grammar, vocabulary, and cultural sensitivities.
Produce only the {TARGET_LANG} translation, without any additional explanations or commentary. Please translate the following {SOURCE_LANG} text into {TARGET_LANG}:


{TEXT}

Describe the solution you'd like

The translation feature should have a model selector and a prompt configuration box.

Describe alternatives you've considered

It's possible that a standalone translation provider app could do this, but that seems heavy-handed compared to just configuring the existing translation functionality in this integration.

Start by locating the existing translation functionality in this integration and tracing how its provider, model, and prompt are currently selected. Compare that flow with the requested model selector and prompt configuration box. Done means translation can use a chosen model and configurable prompt format, including the variables shown in the issue.