Offer to co-maintain Discourse SSO

We use this module on Omnipedia for our community Discourse, and I've had to apply a whole bunch of patches to keep this module functioning. It seems y'all are pretty busy (understandable) so I want to offer to co-maintain this module so we can get various fixes merged, Drupal 11 support merged, and a new release out. Down the line, I'd also like to modernize the code more and add tests.