Move Credentials event bus functionality to publish-by-config

[justinhynes]

The Credentials service was recently updated to support publishing program certificate events to the Event Bus (EB).

At the time, publishing events to the EB required code. There is work being done to enable publishing of events to the EB via configuration.

Work is planned to convert Credentials to a publish-by-config approach. This means we will be deprecating and removing the following settings:

• PROGRAM_CERTIFICATE_EVENTS_KAFKA_TOPIC_NAME: topic names are part of the EVENT_BUS_PRODUCER_CONFIG and a separate setting will no longer be needed
• SEND_PROGRAM_CERTIFICATE_AWARDED_SIGNAL: removed in favor of a single setting (SEND_LEARNING_PROGRAM_CERTIFICATE_LIFECYCLE_EVENTS_TO_BUS) to enable publishing program certificate events to the EB
• SEND_PROGRAM_CERTIFICATE_REVOKED_SIGNAL: (see above)

Work will be tracked as part of an internal 2U JIRA ticket: https://2u-internal.atlassian.net/browse/APER-2966

[justinhynes]

This work was completed near the end of 2023 and this issue can be closed.