FlowETL deployment example

[maxalbert]

In the FlowETL deployment example, the external Postgres database from which the sample data is ingested is currently set up within the same docker stack in which the FlowKit components (FlowDB and FlowETL) are deployed. This is convenient for the example, but does not reflect typical real-life scenarios where the ingestion db already exists because it has been set up externally. To make the example more realistic, it would be better to deploy the ingestion db outside the docker stack.