[APER-3229]
In a previous PR, I created a new utility function named `is_credentials_enabled()` that can be used to determine if use of the Credentials IDA is enabled by config in an Open edX instance.
This PR is some additional cleanup that replaces the direct import and use of the `CredentialsApiConfig` model with the new utility function.
I took some additional time to update some existing log messages to include more info while reducing our need to log PII. I've removed as much use of a learner's username as possible, replacing it with logging the learner's LMS User Id instead.
7f62080c95