Document privileges required by non-root Maria DB users

[p-j-smith]

If I run the SDK tests with credentials for a non-root user to connect to MariaDB, I get the following error:

FAILED test_api.py::test_api - mariadb.OperationalError: Access denied for user 'user'@'%' to database 'api_test'

If I instead connect to MariaDB as root, the test runs okay. It would be super useful to document the privileges required for non-root MariaDB users.

[p-j-smith]

I've just realised that the user will need all privileges for the relevant database(s), and as there are lots of databases created in the tests it's easiest to run the tests as root. Although it might be good if the tests could use a root user to grant the relevant permissions to a user, and then use a regular user when actually running the tests.