Include sixteen auth-client lines by default

auth-client are a required field...

  https://trac.torproject.org/projects/tor/ticket/32563
  https://trac.torproject.org/projects/tor/ticket/31823#comment:16

Tor creates sixteen by default, so doing the same unless our caller specifies
otherwise.

  % cat demo.py
  from stem.descriptor.hidden_service import OuterLayer

  print(OuterLayer.create())

  % python demo.py
  desc-auth-type x25519
  desc-auth-ephemeral-key fhUEgYTR3j4/8MC8aH75WTIKWFOzvKiXURvPHdIXTH4=
  auth-client 1J4LPB+umNA iOGHkI+vpsWJaugbv6akgg EtisFxHd3buXMcl30uxJ8A
  auth-client wbmXMy71u+Q aiFlaQQV3hBPrmOaQ8kXDg HP+ZFqEt0z47F5AVBnyzxA
  auth-client ahHWCcU8INM kQrwT8jZOXAdxiyeVZ/EWw tIBpoOqhvoGhFCOceSLZXA
  auth-client UrnUpDYoCTs 6VC/C7xcIWd4Dtmrj1nKig 1k2hfoPhGPwX4BORgHeDPw
  auth-client 5I03RmlXJps rgdrWYmq02EmMF+v7PMoLw lkxQtmEz3+CVniXM0E16vQ
  auth-client ub0ap7cdghQ gGjmEJTYcw6RGwri2DlPaQ Wz+vnYEc2PmeFxM85lNCcg
  auth-client TLgL1NsDjIU bKuIgs/blO3mL80mC13JDw 8sjbuwv3o9sQTt0yQbhIxw
  auth-client aytYGQGGAkE lqg3uBRYIX9DHjWl8aLmxQ Nsb6dvhnykFJtSyeGekUhw
  auth-client htPYuHAyOsA Wim8CZKo3o2toq+dqeGgMg m6vIoCpQWT0JRR+JgcHIqw
  auth-client oJJr9IpqKpc gwd5SFc0CWtRMAaZaqWQrQ iA8qoyKVXWs2N6DA9WzqiQ
  auth-client EEIi97LqhGA K+Vn6P2dfRgFZXHhgBvX9A 9bXjd6UBUXuBY3/aeNCR5w
  auth-client 1JCG9WKhPKY CgMjZquv+KPLzpqn72uMKQ kC6e5GM/1+2TIvq8kb47Lw
  auth-client 6MuN+1vob4w Wi1ktyiaiOaG6PaLbneydQ OEigSskYEZb8hGqWZMDKlg
  auth-client uOoXx8epem4 /VjgpZzC71Gj6WAXuVXzVw Q4dOW6GYc/JoQrKNLUQmbQ
  auth-client aC9d6RbIr1M FCY56VPOLEktEsQiCDrORQ 0fAhfjriUxnFvbjiTfGDrw
  auth-client 60vj3crxSwg XSytZMniMFUCDYbhyrdhDg 3P5Q5QaI70AvX/d8Wh7Etw
  encrypted
  -----BEGIN MESSAGE-----
  EqEXDglNZxN+TmE6I7U7fd9DM0ue9ys770n6AnH4ga+fLSJ8AOb0lX4XANG9TuFh
  6hyOfGa0joPezoQSeAFf+yk=
  -----END MESSAGE-----