Available google gemini model names are hardcoded

[haesleinhuepf]

We should update the code so that the list of available models is dynamic. I couldn't find how to do this using the Python API. The REST-API allows it already: https://cloud.google.com/vertex-ai/docs/reference/rest/v1/projects.locations.models/list

This sections needs to be updated: https://github.com/haesleinhuepf/bia-bob/blob/2a8492e04010809d0cdb8293f212f77987205473/src/bia_bob/_utilities.py#L369-L370