Create Database Initialization Listener Interface

[jdpgrailsdev]

Tell us about the problem you're trying to solve

The existing code couples database access with connection initialization. The system wants to gate service startup on database creation and migration. Separating these two concerns will make it easier to adapt the code to an application framework.

Describe the solution you’d like

The solution to this coupling is to replace the per-database initialization logic in the existing DatabaseInstance implementations into a series of event listeners which can be invoked by the framework (e.g. Micronaut) at startup to perform the database initialization check. See the "proposed state" portion of the Whimsical diagram for more details.

Acceptance Criteria

• Introduces a DatabaseInitializationEventListener interface
• Implementation event listener class created for each database
• Initialization logic is copied from DatabaseInstance /subclasses to the appropriate listener implementation.