Add GDPR support

[golenkovm]

As of 3.5 Moodle requires GDPR support to be implemented for all installed plugins. See https://docs.moodle.org/311/en/GDPR

Failing core unit tests:

root@cf7f7c4e89bd:/var/www/site# vendor/bin/phpunit --testsuite='core_privacy_testsuite'
Moodle 3.9.11 (Build: 20211108), 2f59059095d9a1779195e2d3df6c19b399413ed3
Php: 7.4.25, pgsql: 9.6.16, OS: Linux 5.4.0-89-generic x86_64
PHPUnit 7.5.20 by Sebastian Bergmann and contributors.

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Time: 49.83 seconds, Memory: 161.00 MB

There were 2 failures:

1) provider_testcase::test_all_providers_compliant with data set "block_grade_me" ('block_grade_me', 'block_grade_me\privacy\provider')
Failed asserting that false is true.

/var/www/site/privacy/tests/provider_test.php:178
/var/www/site/lib/phpunit/classes/advanced_testcase.php:80

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

2) provider_testcase::test_table_coverage
The following tables with user fields must be covered with metadata providers: 
  - block_grade_me_quiz_ngrade (userid)

/var/www/site/privacy/tests/provider_test.php:327
/var/www/site/lib/phpunit/classes/advanced_testcase.php:80

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

FAILURES!
Tests: 1525, Assertions: 10872, Failures: 2.