Preserve order of mentioned users

Signed-off-by: marcin mikołajczak <git@mkljczk.pl>

lib/pleroma/user.ex

@@ -2279,6 +2279,7 @@ def ensure_keys_present(%User{} = user) do
   def get_ap_ids_by_nicknames(nicknames) do
     from(u in User,
       where: u.nickname in ^nicknames,
+      order_by: fragment("array_position(?, ?)", ^nicknames, u.nickname),
       select: u.ap_id
     )
     |> Repo.all()