[Feature]: Start using `InstanceAvailability.NO_BALANCE` in `dstack` Sky

### Problem

When a `dstack` Sky user has no balance, cloud offers are shown as `not available`, which is difficult to decipher.

### Solution

Use the new `no balance` status for offers.

### Workaround

_No response_

### Would you like to help us implement this feature by sending a PR?

Yes