feat: add a custom google backend for sso

[zlwaterfield]

Changes

Our current system stores google-oauth2 uids as emails which makes it so if a customer changes their domain in GSuite, none of their users can login because it's looking against the old email domain. This PR updates our system to use the OpenID sub, which is guaranteed to be a unique and consistent identifier for the user.

It inherits from the existing class so all other functions will fall to the inheritance.

It's implemented in a way that it has backwards compatibility for existing users and slowly migrates them as they login. Over time this custom class could be removed and it be updated to use the default social core get_user_id and setting the settings.USE_UNIQUE_USER_ID = True option.

Here is the social core method: https://github.com/python-social-auth/social-core/blob/master/social_core/backends/google.py#L12-L20

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Does this work well for both Cloud and self-hosted?

Yes

How did you test this code?

Add light tests manually tested:

• existing user with email as uid
• existing user with sub as uid
• new user

[patricio-posthog]

Looks good to me. Thanks for this change, Zach!

[benjackwhite]

Looks good to me. Obviously a little risky change but the code seems solid.