add a --format json option to gally run

[gregoryguillou]

For now when you execute gally run, it displays the output as the underlying commands do. We would like to add a --format json so that instead of that default behavior, that could be named --format text it would create a json file like:

{ "runs":
   {
      "project1": {
         "command": "build",
         "output": [
            "1st line output",
            "2nd line output",
            "...",
            "last line output"
         ]
      },
      "project2": {
      ...
   }
}

The reason for this request is so that we can create a version_production command that would simply return the version that is currently running on production and would return the version. This would enable to easily list all the running version for one environment from gally