Make AWS_SES_AUTO_THROTTLE None by default

[akifd]

The auto throttling is an optional feature, which in my opinion should not be on by default, as it requires additional permissions on AWS side.

My suggestion is to make it None by default and let apps who want to use it set the value to something else. If this is done, version number should probably be bumped to 2.0.0 as it is potentially breaking change.

[pcraciunoiu]

That's a valid point, though perhaps it's also useful to have it on to avoid spamming?

If you want to submit a PR, you are welcome to.