RFC: improve usability by allowing members and admins to be defined as a list

[mariux]

this is a backwards incompatible change that increases usability by changing the members variable and introducing an admins variable each defining a list(string) of usernames instead of a list(map).

members = [ "user1", "user2" ]
admins  = [ "user3", "user4" ]

instead of

members = [
  {
     username = "user1",
     role     = "member",
  },
  {
     username = "user2",
     role     = "member",
  },
  {
     username = "user3",
     role     = "admin",
  },
  {
     username = "user4",
     role     = "admin",
  },
]