Follow-up from "Update headlamp tag 0.39.0 bb.2"

The following discussion from !7309 (merged) should be addressed:

• @andrewshoell started a discussion: (+1 comment)

  @dhilgaertner2 this looks good to me, but can we add a flexible k3s flag in addition to these OIDC flags? We have needed a lot of k3s args historically and it'd be nice to be able to add some when needed. Maybe something like:

  declare -a k3s_args=()
  ...
  --k3s-arg)
    shift
    k3s_args+=("$1")
    ;;
  ...
  # double check string escaping here
  for arg in "${k3s_args[@]}"; do
    k3d_command+=" --k3s-arg \"${arg}\""
  done