Provide helper function to retrieve default coloumns when using `-t`

### Proposal
Add a new helper function to be used in CLI outputs with `-t` that provides the default columns for the command.

### Use-cases
When using `-t` to format a command output users have to declare all the columns they want. In some cases all that is needed is to expand the default output with a few more values, but currently this requires re-declaring all columns.

For example, `nomad node status` outputs the following:

```console
$ nomad node status
ID DC Name Class Drain Eligibility Status
83a42fd9 dc1 laoqui-GDP2M7PY2N false eligible ready
```

To add a new column we would need to do run the command as:

```console
$ nomad node status -t '{{range .}}{{.ID}} {{.Datacenter}} {{.Name}} {{.NodeClass}} {{.Drain}} {{.SchedulingEligibility}} {{.Version}}{{end}}'
83a42fd9-7864-753d-f6b2-42900171fb33 dc1 laoqui-GDP2M7PY2N false eligible 1.5.0
```

If a helper function were available this command could be reduced to:

```console
$ nomad node status -t '{{range .}}{{.DefaultColoumns}} {{.Version}}{{end}}'
83a42fd9-7864-753d-f6b2-42900171fb33 dc1 laoqui-GDP2M7PY2N false eligible 1.5.0
```

Start by tracing the CLI implementation for `nomad node status` and how its default columns are assembled for `-t` output. Identify the relevant output paths and tests, then verify that a helper exposes the default columns for templates without requiring users to redeclare them.

Written by the indexing model from the issue text.