add mix task for deactivating a user by nickname

lib/mix/tasks/deactivate_user.ex

@@ -0,0 +1,13 @@
+defmodule Mix.Tasks.DeactivateUser do
+  use Mix.Task
+  alias Pleroma.User
+
+  @shortdoc "Toggle deactivation status for a user"
+  def run([nickname]) do
+    Mix.Task.run("app.start")
+
+    with user <- User.get_by_nickname(nickname) do
+      User.deactivate(user)
+    end
+  end
+end