Make phone and password kwargs in start

readthedocs/misc/v2-migration-guide.rst

@@ -983,3 +983,4 @@ send_code_request now returns a custom type (reducing raw api).
 sign_in no longer has phone or phone_hash (these are impl details, and now it's less error prone). also mandatory code=. also no longer is a no-op if already logged in. different error for sign up required.
 send code / sign in now only expect a single phone. resend code with new phone is send code, not resend.
 sign_up code is also now a kwarg. and no longer noop if already loggedin.
+start also mandates phone= or password= as kwarg.

telethon/_client/telegramclient.py

@@ -313,9 +313,9 @@ class TelegramClient:
     @forward_call(auth.start)
     def start(
             self: 'TelegramClient',
+            *,
             phone: typing.Callable[[], str] = lambda: input('Please enter your phone (or bot token): '),
             password: typing.Callable[[], str] = lambda: getpass.getpass('Please enter your password: '),
-            *,
             bot_token: str = None,
             code_callback: typing.Callable[[], typing.Union[str, int]] = None,
             first_name: str = 'New User',