Introducing Custom Servers: Deploy production-ready model servers from Docker images

Introduced Custom Servers, a new feature that allows deploying model servers directly from Docker images using a YAML configuration. This bypasses the need for Truss Server for pre-packaged images (e.g., vLLM, Triton) or proprietary Docker images. Key features include a codeless developer experience, full integration with Baseten's ML infrastructure (autoscaling, GPU availability), and support for custom readiness and liveness probes. This extends the flexibility of Baseten's model deployment capabilities.