operator debug uses platform-specific separators in bundle

When `nomad operator debug` is used on Windows, the file paths in the resulting `.tar.gz` file use the platform-specific separator. This results in a single flat hierarchy like this when they're opened up on Unixish machines:

```
nomad-debug-2021-03-09-014419Z\nomad\0003\nodes.json
nomad-debug-2021-03-09-014419Z\nomad\0003\operator-autopilot-health.json
nomad-debug-2021-03-09-014419Z\nomad\0003\operator-raft.json
nomad-debug-2021-03-09-014419Z\nomad\0003\operator-scheduler.json
nomad-debug-2021-03-09-014419Z\nomad\0003\plugins.json
nomad-debug-2021-03-09-014419Z\server\us04pB-nmd1.global\agent-host.json
nomad-debug-2021-03-09-014419Z\server\us04pB-nmd1.global\goroutine-debug1.txt
nomad-debug-2021-03-09-014419Z\server\us04pB-nmd1.global\goroutine-debug2.txt
nomad-debug-2021-03-09-014419Z\server\us04pB-nmd1.global\goroutine.prof
```

A quick glance at the code suggests we might be handling the paths as strings at once point, but I'm not sure whether or not that makes a difference. At the end of the day this is at best a papercut, so long as no one handles the paths as strings instead of paths (ex. `\nodes.json` could get read in as an escaped newline with an unforgiving script).

Start with the implementation of `nomad operator debug` and trace how paths are constructed before they are written into the `.tar.gz` archive. Reproduce the command on Windows and inspect the archive on a Unix-like system; done means archive entries use portable separators and preserve the intended directory hierarchy.

Written by the indexing model from the issue text.