Run functional tests with datastore_mysql_import enabled

[paul-m]

Currently, tests do not run with datastore_mysql_import module enabled, so there are no functional tests which support it.

This PR:

• Converts (most of) the dkan DatasetTest functional test to a Drupal BrowserTestBase test: DatasetBTBTest
• Subclasses DatasetBTBTest to MySqlDatasetBTBTest which enables datastore_mysql_import and runs all the same tests.
• DatasetTest::testResourcePurgeDraft() remains in the old DatasetTest class, because it depends on moderated_content_bulk_publish module, which has an incomplete config schema which fails BTB testing.

Since the new tests now use the real-deal services, and use some more strict validation from BTB, we discover that our tests (and modules) were buggy and needed some attention.

• Config schema did not validate, so some modules would not enable.
• Within DatasetBTBTest::getData() we call ValidMetadataFactory::get() which validates the JSON. Our test JSON was not validating. See the @todo in that method.

TODO in follow-ups:

• Determine how to move DatasetTest::testResourcePurgeDraft() to be a BTB test.
• Figure out how to get a useful assertion within DatasetBTBTest::getData().