[Improvement] Support event dispatching for catalog connection tests

### What would you like to be improved?

`CatalogEventDispatcher` currently delegates both pre-create and existing-catalog connection tests without emitting pre, success, or failure events. This prevents listeners and auditing integrations from observing these operations.

### How should we improve?

Add event dispatching for both `testConnection` methods and cover their success and failure paths with unit tests. Event payloads must not expose connection properties or credentials.

Start by locating CatalogEventDispatcher and its two testConnection methods, then inspect the surrounding event-dispatching patterns and existing unit tests. Add coverage for pre, success, and failure paths for both connection-test variants, verifying that event payloads omit connection properties and credentials.

Written by the indexing model from the issue text.