Refactor S3 configuration to be compabitle with ADR and operator-rs implementation

[maltesander]

As a user of the Spark operator I want to refer to an existing S3 connection as specified in stackabletech/documentation#177

This is done when

the operator is compatible with the ADR linked above to configure our S3 storage (as per the example below)
documentation, examples and integration tests have been updated

See stackabletech/operator-rs#377 which is required for this