add support for SESv2 under feature flag

[fergusdixon]

Fixes #229

This is not adding support for any new features not previously supported by django-ses
This is just moving the current raw email logic to the new send_email method, which has some enhancements to cross-account verified identities under the hood

Personally, my motivation came from running into a similar issue to this aws/aws-cdk#18964 (comment)

New features can be added in follow up PRs

I've tested this in my own environments and works end-to-end

[pcraciunoiu]

Thanks so much for your work on this, and adding tests! Only small comments.

Not sure what's going on with GitHub canceling the job runs, I'll try rerunning again later. Hopefully the tests will pass.

[pcraciunoiu]

So this is referring to modifying django_settings? Any plans to fix this in the current PR?

[fergusdixon]

This was kinda copied from the existing tests

django-ses/tests/test_backend.py

Line 94 in 24fee37

# TODO: Fix this -- this is going to cause side effects

https://github.com/fergusdixon/django-ses/blob/24fee37f2600ea008b296fe958404df11f21d9ec/tests/test_backend.py#L94
I feel I do a decent job cleaning up during the tearDown, so will remove the comment

[fergusdixon]

Thanks so much for your work on this, and adding tests! Only small comments.

Not sure what's going on with GitHub canceling the job runs, I'll try rerunning again later. Hopefully the tests will pass.

Thanks for the comments, will work on it today
Any preference on how you want me to update the changelog? I just added what seemed reasonable but not sure how your releases work.

As for the jobs, I'm happy to update to ubuntu20 in this PR too?:

[pcraciunoiu]

Merged in #269, releasing as v3.3.0 now