Adding new changeset arguments in `before_action`

update :foo do
  require_atomic? false
  
  accept []

  argument :arg1, :string, allow_nil?: false

  change before_action(fn changeset, _context ->
    record = changeset.data

    nested_resource = NestedResource.create!(%{parent_id: record.id})

    Ash.Changeset.set_argument(changeset, :nested_resource_id, nested_resource.id)
  end)

  change fn changeset, _context ->
    dbg(changeset.arguments)

    changeset
  end
end

arguments #=> %{
  nil: "0198908a-c4ca-7c4f-831e-b67ea589f4c8",
  arg1: "description"
}