Document purpose/usage of LOG_MINING_FLUSH in oracle connector docs

## Feature request or enhancement

**Which use case/requirement will be addressed by the proposed feature?**

This is hopefully a straightforward request for additional documentation. In our production environments we have rules around creating new schemas/tables. We typically create the debezium_signal table as part of our initial setup which is a formal request.

Debezium, for Oracle instances, creates a LOG_MINING_FLUSH table within the Debezium schema. While this isn't an issue, I've often gotten questions around why this table is there and what it is doing. I think creating the table automatically is fine but would be helpful to just have a short snippet in the docs that explains that Debezium is creating it and what it is using the flush for.