Expose members of a group proposal

[MartinBenediktBusch]

Overview

When commenting on a propoal all members of a group in addition to the author should get displayed.

Expected Output

Author data {
      optionId: 'df4e876d-0099-49e3-b1bb-eba0c6c9ed06',
      registrationId: '6133018b-24a4-4440-ac39-e8927198e189',
      user: {
       id: xxx
      username: xxx,
      firstName: xxx,
       lastName: xxx
    },
      groupId: 'aad04a6b-7759-435a-bdab-3db7c44496f2',
      users: [
        {
       id: xxx
      username: xxx,
      firstName: xxx,
       lastName: xxx
    },
         {
       id: xxx
      username: xxx,
      firstName: xxx,
       lastName: xxx
    },
      ]
    }