config(manifest): omit most of empty config items

[rinor]

Instead of getting all config items on manifest, we want just what is configured/set.

• right now we have:

  {
  "Args": [
  "node"
  ],
  "DisableArgsCopy": false,
  "BaseVolumeSz": "",
  "Boot": "",
  "UefiBoot": "",
  "Uefi": false,
  "BuildDir": "",
  "CloudConfig": {
  "BucketName": "",
  "BucketNamespace": "",
  "DomainName": "",
  "StaticIP": "",
  "EnableIPv6": false,
  "Flavor": "",
  "ImageType": "",
  "ImageName": "",
  "InstanceProfile": "",
  "Platform": "",
  "ProjectID": "",
  "SecurityGroup": "",
  "Subnet": "",
  "Tags": null,
  "VPC": "",
  "Zone": ""
  },
  "TargetConfig": null,
  "Debugflags": null,
  "Dirs": null,
  "Env": null,
  "Files": null,
  "Force": false,
  "Kernel": "",
  "KlibDir": "",
  "MapDirs": null,
  "Mounts": null,
  "NameServers": null,
  "NanosVersion": "",
  "NightlyBuild": false,
  "NoTrace": null,
  "ManifestPassthrough": null,
  "Program": "mypkg_0.0.1/node",
  "ProgramPath": "",
  "RebootOnExit": false,
  "RunConfig": {
  "Accel": false,
  "Bridged": false,
  "BridgeName": "",
  "CanIPForward": false,
  "CPUs": 0,
  "GPUs": 0,
  "GPUType": "",
  "Debug": false,
  "Gateway": "",
  "GdbPort": 0,
  "Imagename": "",
  "InstanceGroup": "",
  "InstanceName": "",
  "IPAddress": "",
  "IPv6Address": "",
  "Klibs": null,
  "Memory": "",
  "Vga": false,
  "Mounts": null,
  "NetMask": "",
  "Nics": null,
  "Background": false,
  "Ports": null,
  "ShowDebug": false,
  "ShowErrors": false,
  "ShowWarnings": false,
  "JSON": false,
  "TapName": "",
  "UDPPorts": null,
  "Verbose": false,
  "VolumeSizeInGb": 0
  },
  "LocalFilesParentDirectory": "",
  "TargetRoot": "",
  "Version": "0.0.1",
  "Language": "",
  "Runtime": "",
  "Description": "",
  "VolumesDir": "",
  "PackageBaseURL": "",
  "PackageManifestURL": ""
  }

• desired output:

  {
  "Args": [
  "node"
  ],
  "Program": "mypkg_0.0.1/node",
  "Version": "0.0.1"
  }

• what this pr provides:

  {
  "Args": [
  "node"
  ],
  "CloudConfig": {},
  "Program": "mypkg_0.0.1/node",
  "RunConfig": {},
  "Version": "0.0.1"
  }

  Can take care of removing also "CloudConfig" and "RunConfig", but not sure if it's worth it.