add OfflineManagementClient.executeCli(String)

[Ladicek]

Some local CLI operations can be run offline. For that, we'd need something like OfflineManagementClient.executeCli(String). That shouldn't be terribly hard to add.

The only thing is that I'd like to have a unified CliException for both online and offline CLI, yet the existing CliException is in the ...online package. Not sure how to deal with that. Probably just give up this goal and use a different exception, e.g. OfflineCliException.