Report Skaffold panics through metrics

The Cloud Code for VS Code team noticed that their interactive debugging tests were failing. The ultimate cause was that Skaffold was panicking as a channel was being closed multiple times (fixed in #6714). This error had gone uncaught and made it into a release.

We should catch panics and report them through our metrics so that we can be alerted if there is a major error being encountered by our users.

### Proposal

1. Define a new StatusCode (`PANIC = 1`?)
2. Trap panics in our top-level command and
- submit a special metric if metrics are logged
- emit a `terminationEvent` event to report up through Cloud Code