HTML emails are sent with text/plain content-type

[dylwhich]

No description provided.

[bitbyt3r]

If we only want to send html email then we can fix this by just changing the content type here: https://github.com/magfest/tuber/blob/main/backend/tuber/aws.py#L130

We might want to generate both a plaintext version and a rich html version and pass both to AWS for maximum compatibility. I didn’t feel like doing that when I originally put this together, so I just pretend it’s all plaintext.