Add connector type to source info

The identifier name was changed in DBZ-306 ticket, I propose to allow an user to define the identifier name (identity.field or identifier.field setting with id value by default) in settings of the MongoDB connector.

This may be necessary for the case when a sink connector is subscribed to topics of MongoDB and Postgres connectors. In this case it is difficult to distinguish primary keys of the databases, and the primary key of MongoDB requires additional work on the transformation of the identifier in contrast to the primary key of PostgreSQL.

This requirement has been addressed by adding a field with the connector type to the source info block of CDC messages, allowing consumers to apply specific handling if needed.