[Doc] Add Debezium Architecture to downstream documentation

The upstream documentation provides an overview of the deployment architecture of Debezium [1]. This information should also be provided in the downstream, this might fit well in the Getting Started guide. Most importantly, the classification of the Debezium being a source connector as this is crucial information for users just starting out and learning Debezium.

[1] https://debezium.io/documentation/reference/1.1/architecture.html