Make OAuthError extend GenericError

[frederikprijck]

Description

For consistency, this PR makes OAuthError extend GenericError, which still extends Error.

References

636

Checklist

• [x] I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• [x] All active GitHub checks for tests, formatting, and security are passing
• [x] The correct base branch is being used, if not the default branch