Add `subnet` command which contains all subnet-related commands. Add
sub-commands:
* `create` for creation;
* `remove` for removal;
* `get` for reading;
* `admin` for admin management;
* `client` for client management.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Define `ControlService` for IR similar to the one from storage node. Add
`HealthStatus` RPC which returns health status of the IR application.
Implement getters, setters and methods to sign/verify the messages.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
