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

[randomir]

Something like:

$ dwave config -f /path/to/file -p profile-name set solver DW_2000Q_6
<solver set to DW_2000Q_6 for profile-name>

$ MY_TOKEN=$(dwave config get token)
<api-token stored in an env var>

$ 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
<default solver topology set to pegasus>