Sink Notification: Connector name in the additional data [DBZ-6819]

Migrated from [DBZ-6819](https://issues.redhat.com/browse/DBZ-6819)

h2. What Debezium connector do you use and what version?

2.3.2.Final
h1. Feature request or enhancement

In the case of an initial snapshot, I'd like to have the connector name in the event's payload (as it is documented for the Incremental Snapshot):

{{{ "id":"6d82a3ec-ba86-4b36-9168-7423b0dd5c1d", "aggregate_type":"Initial Snapshot", "type":"COMPLETED", "additional_data":{ "connector_name":"my-connector" } }}}

Start by comparing the initial-snapshot notification with the documented incremental-snapshot event and trace where the additional_data payload is assembled. Done means the initial snapshot event includes connector_name with the expected value, with coverage for the resulting payload.

Written by the indexing model from the issue text.