Create CLI for config read/update, `dwave config {get|set|list}`

Something like:
```
$ dwave config -f /path/to/file -p profile-name set solver DW_2000Q_6

$ MY_TOKEN=$(dwave config get token)

$ dwave config -p test list
test.solver = ...
test.endpoint = ...
```

And then after #426, even something like this:
```
$ dwave config set defaults.solver.topology.type pegasus

```