Add Mistral Small 4 to Ollama Models

Mistral did recently release Mistral Small 4 (see: https://mistral.ai/news/mistral-small-4) as the successor to the very successful Mistral Small line (where, previously, the last installment was Mistral Small 3.2, which is almost a year old now).

The model is, again, fully open source and weights are already available on Huggingface: https://huggingface.co/collections/mistralai/mistral-small-4