Error if AWS_SES_AUTO_THROTTLE set to None

If I set AWS_SES_AUTO_THROTTLE to None in my django settings, I get an error on initializing the SESBackend, I believe because of this commit coercing the setting to a float.

The README instructs users to set AWS_SES_AUTO_THROTTLE to None to turn off automatic throttling, as does a comment

Looks like this could be fixed by doing this coercion here or falling back to 0 here

In case it’s helpful to see a traceback:

Traceback (most recent call last):                                                                                                                                                                   
  File "/usr/src/app/./manage.py", line 15, in <module>
    execute_from_command_line(sys.argv)                                                           
  File "/usr/local/lib/python3.9/site-packages/django/core/management/__init__.py", line 419, in execute_from_command_line
    utility.execute()                                                                             
  File "/usr/local/lib/python3.9/site-packages/django/core/management/__init__.py", line 413, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)                                   
  File "/usr/local/lib/python3.9/site-packages/django/core/management/base.py", line 354, in run_from_argv
    self.execute(*args, **cmd_options)                                                                                                                                                               
  File "/usr/local/lib/python3.9/site-packages/django/core/management/base.py", line 398, in execute
    output = self.handle(*args, **options)                                                                                                                                                           
  File "/usr/src/app/scheduler/management/commands/send_test_email.py", line 24, in handle
    send_email(                                                                                   
  File "/usr/src/app/authapp/utils.py", line 70, in send_email
    email.send()                                                                                  
  File "/usr/local/lib/python3.9/site-packages/django/core/mail/message.py", line 284, in send
    return self.get_connection(fail_silently).send_messages([self])                                                                                                                                    File "/usr/local/lib/python3.9/site-packages/django/core/mail/message.py", line 241, in get_connection
    self.connection = get_connection(fail_silently=fail_silently)
  File "/usr/local/lib/python3.9/site-packages/django/core/mail/__init__.py", line 35, in get_connection
    return klass(fail_silently=fail_silently, **kwds)                                                                                                                                                  File "/usr/local/lib/python3.9/site-packages/django_ses/__init__.py", line 63, in __init__
    self._throttle = float(aws_auto_throttle or settings.AWS_SES_AUTO_THROTTLE)
TypeError: float() argument must be a string or a number, not 'NoneType'   

[curtismorales]

My apologies on not wrapping up this conversation and fix back in August! Thanks @lukeburden for bumping it!

[lukeburden]

@pcraciunoiu amazing, thanks for that!

And no worries @curtismorales, thanks for the contribution.