[feature request] get expect output with command

Currently I can only generate the output (`Stack Outputs`) as `output.json` when run the command `sls deploy` with this plugin.

But I'd like to get the output (Stack Outputs) as json on-fly, for example, if I can run 

```
sls info -v --output json
or
sls info -v -o json
```

That will be convenience. 

cc: @sbstjn  @anttiviljami