[k8s] Resource availability check in sky launch

[gaocegege]

Currently, the cloud kubernetes defaults to using 2 CPU and 2 GB of memory for task creation, which can be inconvenient. This is particularly true with the new feature for deploying on existing machines or using sky local up.

When users set up a development cluster on their local machine, they typically expect to utilize all available resources.

The optimal solution, as mentioned in the comments, is to implement an availability check. https://github.com/skypilot-org/skypilot/blob/master/sky/clouds/kubernetes.py#L244