Introducing: Region selection

What this post added

Introduced the capability for users to specify the cloud region for their Modal Functions. This is achieved through a new `region` parameter in the `@app.function` decorator, which accepts region strings with varying granularity (e.g., 'us', 'us-east', 'us-east-1'). The system supports specifying multiple regions for increased flexibility and faster cold starts. This feature is available on Team and Enterprise plans and addresses use cases related to regulatory compliance, cost optimization (egress fees), and latency reduction.