Add GDPR support

[TamaraGunkel]

Hello,
it would be great if you could implement the new Privacy API. We are using the module and thus it is important for us that you implement it.
Thanks!

[tlock]

Specifically,

To re-run:
vendor/bin/phpunit "provider_testcase" privacy/tests/provider_test.php

provider_testcase::test_table_coverage
The following tables with user fields must be covered with metadata providers:~

• activequiz_groupattendance (userid)
• activequiz_attempts (userid)
• activequiz_grades (userid)